I have profiles on LinkedIn, MySpace and Facebook. I use Twitter. Here’s why.

• The 140 Character Limit
  The 140 character limit is the killer feature that makes Twitter great.
  • It (usually*) prevents people from using Twitter for things they should be doing elsewhere, like on their blogs — ie., writing stuff that can’t be expressed in 140 characters.
  • It (usually*) forces people to write concisely.
  • It (usually**) makes it possible to interact with large numbers of people without consuming inordinate amounts of time. It may be the best tool available for the common man to engage the “gurus” in conversation, because it prevents you from gobbling up too much of their time per message.

  * There are exceptions to the rule — people who split long messages between several tweets. But most people understand that such messages belong on their blogs. They can link to their long blog posts from Twitter in one tweet.
       ** The exception to this rule is people who post a lot more tweets than they have useful things to say.

• Twitter does one thing only: short messages.
  The problem with the other sites is that if you really just want a “wall” (to use the Facebook terminology), … well, tough luck. You’ve gotta have the whole profile. Sure, you don’t have to fill everything in, but your profile is formatted based on the assumption that you will.
• Twitter does what it does in only one way.
  On Facebook, half your family uses one widget to track who they’re related to and half use another. Half your friends use one widget to mark all the places they’ve traveled and lived, and half use another. If you want to display your family tree or compare travel histories, you’ve gotta clutter your profile with duplicate widgets or leave half your friends and family out.

There are times when I’d like to be able to post a little more info on my Twitter profile, but honestly, I hope they never allow it — it’d probably be the first step down a slippery slope to being just another social site.