I wonder if its possible with SMF.
I've two words for you: Adblock Plus plug-in custom filter. f*ck, that's more than two....
Outside of that, the content filters for Google Adsense can be used to prevent their ads from appearing.
I'm sure you've had this experience:
1. You are used to viewing your favorite sites sans ads.
2. When you use someone else's computer, and see the ads, the sites suddenly seem UNfamiliar.
Sometimes it is very disorienting, even though I KNOW the layout of the site and should be able to focus on the content, not the ads.