Here are my impressions of Twitter as compared to Facebook after a few weeks of learning. (Originally to my friend on Facebook.)

It's like Facebook, except you can only write on your own "wall", your profile must be less than 160 characters, there's no support for photos or videos or groups or SuperPoke or giving birthday gifts, they use text interrupting @, #, and RT symbols like Perl, and I follow 500 strangers instead of 50 friends.

But it offers an open API, has less "controversial" terms of use, produces a huge volume of content, is useful for business, and satisfies my strange desire to know when Shaq is stuck in LA traffic or what Lance Armstrong had for dinner.

Of course the best service is FriendFeed, but not enough people use it.