The real problem reddit has is that it's community, which can be amazing at times, has grown used to a great user experience when it comes to advertising - the lack of it that is. Just ignore the box on the right and the occasional sponsored link in the top box. Should a flash-based ad appear in the right-hand box there'll be a front-paged topic on it in an hour. reddit has treated it's users well, but they baulk at the slightest change in that - and herein lies the real problem to monetising reddit. reddit has to monetise while keeping it's community happy. Since community happiness and advertising seem to be pretty much polar opposites it seems to be impossible.
What I'd do is increase advertising aggressively for non-logged in users, reduce it greatly for registered users and keep the option to remove it completely for gold members. Hopefully those that really hate advertising would sign up for gold, however there is probably a correlation between those that make the most noise about advertising and those that wouldn't do that as they don't believe in paying for things on the internet - completely unfounded but a gut feeling.
> Sure it would piss off a lot of users...but it's not like people would abandon a site, just because there are a few more ads present.
Being a technical audience AdBlock (already is but) would be widely used rendering it useless. I know reddit was monitoring adblock usage at some point - I'd like to know the results of that.