There's a classifieds section in the Second Life 1.7 Preview, expanded from the previous version with more features like the ability to publish from profile. I think most of the ads so far from the current 1.6.x generation have been of a commercial nature, but I see a future with a Personals section, maybe Announcements (like "HAPPY REZDAY!") and even a Lost Pets section for when Jeffrey Ventrella lays the smackdown on the pixelhaus. The SL Forums serve many useful functions but they are inherently disconnected from SL itself, as only a small population is estimated to read it, even fewer still are posters. It's important to keep all the voyeurs in mind. Often, I will get an IM referencing something I said on the forums by someone who read and didn't reply. I can't say there'll usefully be a time when the forums are actually inworld, because their framework is too bulky. Microchatboards, though, are easily envisioned.
Telehub advertising is jaggy and non-networked, so if you drop your notecard and texture in one 'hub, you'll have to fly to the next to do the same, and the next?there is an archaic charm about it, however. Well, with flying included. So many times I've TPed to a TH and collided with others I know, and then we stay around and chat and more people come along and soon enough there's a crowd. Interestingly enough, this tends to more frequently happen (anecdotally) on aerial hubs like Oak Grove and Mauve. I wouldn't totally discount their usefulness, altho I still say SCROO 'EM!