Personally, I have no problem with ads. Alternatively, I also have no problem making a "small one-time donation" in order to keep the site up and running.
My only reservation is this: if it were necessary to make a one-time contribution in order to post or view messages, it's possible that 1st-time visitors who just happened to find the site wouldn't want to pay, and would therefore not post, or visit again. This would make the board less interesting/lively/diverse/etc.... Maybe free-to-view but donate-to-post, which would draw people in? Or make donations optional? I donno...
What about allowing those who donate to view the site without ads... I assume thats possible to do. That might be more (programming/site maintenence) trouble then it's worth, though.
Ok, I'll stop brainstorming now.
-e.