And where do those ads lead? Usually to a forum thread where members are playing/raiding an MMO together, or discussing a topic of great interest, or selling a service like painting portraits, web hosting, or resume editing (and in one or two cases, to a discussion of a particularly zeal-inspiring anime series).
Some purely parodic examples can be found here:
http://acapella.harmony-central.com/showthread.php?2332472-A...
And here is the current roster of ads, though many are from external advertisers and hence less funny:
http://forums.somethingawful.com/adlist.php
(Note that "goons" is the moniker for forum members, and many ads target them specifically with "goon discounts" and so on.)
Marketers with an attitude and something of a free hand could take a leaf from them.