As I said before, the main goal of this site is real chat with real people. All other ideas are secondary to this goal. So let's go into detail of what I need to get people talking.
Forums. The forums will be the central place for chat. I plan on using the forum module that comes with Drupal and add some contrib modules and tweaks to get the functionality people are used to from other sites.
Private messaging I'm not a big fan of private messages and prefer to use email, but I know it's something a lot of users like. So I'll add privatemsg for that.
Chatting I'd like to have an IRC like chat going. I thought about interfacing with an actual IRC channel but the various JS offerings look like a much better alternative. I had a look at the demos of YShout AJAX Chat and chatbox but the demo of phpfreechat really impressed me. It's not native Drupal but rather an integration of another OS app. I want to try and avoid that where possible, but I like this one so much better than the others that I'm going to go with it for now. chatroom has potential as a native Drupal solution, but it's not ready yet. I'll keep an eye on it and may change at some point.
WYSIWYG I'm haven't decided, yet, on what, if any, WYSIWYG editor to use. I may leave this decision until I get some users and see what they want. Or maybe start with something simple like BBCode or Quicktags instead of more complex ones like TinyMCE or fckeditor
Voting and reviews
After looking at Webchick's excellent article I've decided to go with userreview for nodes where I want both comments and rates, such as business links. I might also end up using Vote up/down Package if I decide to go for a Digg like structure on some content.
Classifieds
I want to have a place where people can place classified ads. I know I talked with someone who had a custom module for this that they were thinking of releasing, but I can't remember who, now... If I can't track that down, I may just use a combination of CCK and views.