I'm dubious. I don't use reddit, but I just skimmed the site. You're totally right, reddit has done a shit job allowing people to advertise. That being said, I have some experience with monetization, and forum traffic, dominated as it is by page refreshes, monetizes like shit. For starters, pv per user is way higher than almost any other type of site. All display advertisers cut individual users off pretty quickly -- IME often under 3 pv per day -- after which you're purely displaying remnant inventory at $.1 to $.3 ecpm.
That said, they should immediately experiment w/ adsense, pubcenter, ideas ala stack overflow of embedding amazon referrals onto all books (not at all obnoxious IME), and some of the better display advertisers. Most of these are free and come with basically no commitment so why not. Also, they should embed quantcast's tracking pixel to get some idea about their demographics in a much cheaper fashion than comscore (NB: this could be misconstrued as an advertisement but I think it's good advice.)
That said, they should immediately experiment w/ adsense, pubcenter, ideas ala stack overflow of embedding amazon referrals onto all books (not at all obnoxious IME), and some of the better display advertisers. Most of these are free and come with basically no commitment so why not. Also, they should embed quantcast's tracking pixel to get some idea about their demographics in a much cheaper fashion than comscore (NB: this could be misconstrued as an advertisement but I think it's good advice.)