[grag]

I interviewed a bunch of reddit users for my senior thesis. One thing I found was that the karma system really encouraged participation (not too surprising but worth considering if your building a social news site).

Check out http://www.thesixtyone.com. It's a great example of how you can instill a social media site with a really fun, game-like quality. Not sure if you want to go in that direction, but still worth checking out.

As far as spamming and moderation, I wouldn't worry about it too much if your just getting started. I probably wouldn't even do email validation to begin with since you want the barrier to be low when your trying to attract your first users. You can always add that stuff later when the need arises.