I think Reddit had a good model in regards to revenue generation (nonintrusive adspace on the page and donations via gilding, although I don't like the idea of locking out site features for non-gilded members. The biggest issue they've run into so far is taking the profiteering a tad too far and now they're running into issues of trying to monetize celebrity interviews and the like.
I dunno, I like the idea of running a site entirely on donations, and if this site turns out to be something I revisit regularly, I would agree with Steve and definitely be on board for an optional regular monthly donation. I just wouldn't necessarily want "premium features" for paying members, the content itself should be enough to sell people on the donations, NPR and PBS have existed for a long while on that same business model. In PA, for instance, we have no subsidies for public broadcasting and the NPR stations here are still very successful and my and a lot of people's favorite stations.