Social Games

Since social games are typically considered casual games, I thought I would start this topic. It is also relevant to a game I am working on.

What are some of the core elements of game design for social games? I am paritcularly interested in:

• The balance between drawing people to your game (e.g. via posts to a wall, tweets, etc.) and bugging people to death
• How to keep gameplay moving fast enough to be meaningful in a gameplay session but slow enough so the player can't conquer the world in 1 day

Any comments?

Robert