I recently wrote this up and thought I would submit it here as well. Basically, it's a practicle guide to advertising on forum sites. Here it is for your consideration.

I've decided to write this up for those looking to monetize their forums with adsense. There are a lot of great articles out there but I wanted to share my experiend with it on forums specifically. Keep in mind that even though this is geared towards vBulletin that the principals can be applied to any forum software. Much of this is subjective to your personal tastes, this is my experience and what has worked best for me. Your feedback and comments are welcome.

SEO Your Forums
It is best to first make sure your board is SEO'd, even if it's just basic mod_rewrites for redirects, turn those ugly looking URL's into informative, content rich page titles. A couple of free mods for VB can be found here http://www.vbulletin.org/forum/showthread.php?t=91324 to SEO your forums and http://www.vbulletin.org/forum/showthread.php?t=100435 for a great sitemap generator which will really help deliver your content to search engines.

There is also a paid product available for vBulletin called VBSEO which many people have reported a great experience with. It's very comprehensive and has loads of options and the creators appear to have an excellent knowledge of SEO. It's not cheap but in the long run it can pay itself off over and over again.

Deliver different ad schemes to your guests
Most forum guests out number registered users by a marginal amount. This is to your advantage and the base of your targeted audience. Many believe that targeting ads towards registered members fall flat because most registered and experienced forum surfers learn to ignore them.

With this in mind, removing ads for your forum members creates a more pleasant surfing experience which keeps them coming back to a cleaner looking forum. There are a couple of considerations to this though, one is that removing ads from members can reduce the eCPM and will result in fewer impressions though it will most likely cause an increase in the CTR. This can be a trade off depending on the sort of ad compaign you choose to run.

Alternatively, some webmasters choose to serve ads to both by leaving a minimum campaign of ads for members while boosting it up for unregistered users.

Look and feel of your ads
Making your ads look a part of your forum is important. Ads that stand apart from your site design are much easier to tune out. Ads that share the same background color and font are the most successful, also matching the border color with the backgroud color makes it look less like an ad and more like site content.

Ad Placement
Google has some great recommendations for forum ad placements here http://adsense.blogspot.com/2005/10...ceid=ASO&subid=us_en-link-opttips&medium=link

To add Adsense to the second post of each thread see here http://www.vbulletin.com/forum/showthread.php?t=157022

Likewise, you can add your banner code to most templates to taste. The most common are forumdisplay, showthread, navbar (will place ad on the top of everypage) and footer.

Adsense Search placement
Utilizing googles Adsense Search is another way to increase your revenue. Something I've recently implemented is putting the google search code at the top for guests. Leaving the default board search feature off for guests will promote the use of it and reduce server load. Here is the code for VB to put it at the top of your forum for guests only:

In the navbar template find:
<!-- / nav buttons bar -->
Add your customized Adsense Search code under: (change 1, 3 to your group ID's for unregistered users and users awaiting confirmation)
<if condition="in_array($bbuserinfo['usergroupid'], array(1, 3))">
<!-- SiteSearch Google -->
code here
<!-- SiteSearch Google -->
To add Adsense to your default search dropdown see here http://www.forumtools.net/t100-add-google-adsense-search-to-your-navbar-dropdown.html

Adsense Terms of service
It is very important to understand and comply with the Terms of Service provided by Adsense. Failure to comply can and most likely will result in the termination of your Adsense account. A quick search for [ame="http://www.google.com/search?hl=en&lr=&safe=off&rls=GGLD%2CGGLD%3A2004-36%2CGGLD%3Aen&q=banned+by+adsense"]banned by adsense[/ame] at the time of writing this article renders 492,000 results which is pretty self explanitory.

Other major advertising companies
With the exception of Fastclick all of the sites below make no mention of NOT placing ads on forums. However, most require that their ads are placed [ame="http://www.google.com/search?hl=en&q=above+the+fold"]above the fold[/ame]. Contextual advertisers such as YPN and Adsense explicitly say that their text ads cannot be combined on the same pages.

Casale http://casalemedia.com/31539.html
Budsinc http://www.budsinc.com/content.htm
Fastclick http://www.fastclick.com/publishers/agreement.html
Burstmedia http://www.burstmedia.com/release/join/eligibility_req.htm
YPN https://publisher.yahoo.com/legal/prog_policy.php
Chitika https://chitika.com/mm_terms.php?application=true
Tribal Fusion http://www.tribalfusion.com/SmartPublishers/contract.html

Getting accepted into the majors with a forum site
This is not always an easy task, certain advertisers such as YPN and Adsense rarely deny a site and their TOS is fairly forgiving, allowing the publisher to place their ads where ever they want. Getting into one of the other sites listed above is a not nearly as easy.

One of the reasons for this is that forum sites have a lot of sporradic impressions that are not easy for the publisher to track or target, especially on a dynamic site. This is one of the reasons so many forum sites get denied or get their accounts terminated.

Setup a static and informative home page
When a publisher views your site, they are looking for static content related to your site and target audience. Just sending them a link to your forum will mostly likely result in a generic letter of denial.

Setting up a portal or a static (html) home page for your site will do wonders. Try to be as informative as possible while keeping in context with what your site is all about. Articles that are listed on the front page can be helpful as well, even if it's just grabbing a post from somewhere on the site and publishing it.

Publishing ads on new forums
Before a forum site is able to generate revenue it is best that it's populated with both users and posts. Placing ads when starting an unpopulated forum gives the appearance that the site is only there to make money and can potentially turn users off to the site.

A new sensation that is becoming quite popular is [ame="http://www.google.com/search?hl=en&lr=&safe=off&q=pay+to+post+on+forums"]paying for posts and registrations[/ame] to boost a new site. Most of these places will charge a reasonable amount to register users and create posts that are relevant to your site. This may be a good avenue for those who don't want to pour a lot of money into advertising.

With the exception of YPN and Adsense, most publishers require several thousand unique impressions per month before a site will be considered.

Cheating the search engines
Trying to trick search engines is probably the worst thing for a site. Although it may go unnoticed for a little while, eventually the site will either get caught and thrown into google's sandbox or have your Adsense account terminated and banned.

Things to consider; [ame="http://www.google.com/search?hl=en&lr=&safe=off&q=google+cloaking"]cloaking[/ame] and [ame="http://www.google.com/search?hl=en&lr=&safe=off&q=google+keyword+stuffing"]keyword stuffing[/ame] will usually get sniffed out by the search engines which in turn will severely hurt the site's placement and page rank. Though they are easy to implement and tempting, it can only serve to harm the site in the long run. Search engines have become very smart and can easily detect this.

Doing the right thing
By setting up a well SEO'd, easy to navigate site with interesting and targeted content, your site get noticed, search engines have become proficient at spotting this. Members will spread the word and backlinks will get around improving your page rank and indexing.