Hmm maybe some should consider creating a blank forum per say or a Sponsor forum and simply use image code to show their ad or ad code from your software of choice? It can be a work around for a few that use ads I know and anyone else all you need to do is think... "What can I display there to rid our site of the gap yet will be helpful or beneficial at the same time?" it could be current products for example if you have a store, show a popular product such as a shirt, coffee mug or other heck whatever you can think of your all creative in different ways

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If users don't like the ads remind them they pay the bills in a nice way OR that there's plenty of software albeit add-ons for Firefox or other that can rid them of ads on all sites heck there's even a GreaseMonkey script that lets you hide all vBulletin signatures on any and every forum if you wish.
Just thought it might spark some ideas so brainstorm everyone!