I've been using Twitter for two years. I check it almost everyday and follow about 150 people. It's a unique social graph for me in that I follow almost no friends or colleagues. I don't use it to interact, I use it to be informed and to learn. By the way, Fred Wilson has been writing some interesting stuff on the different social graphs we use and what he calls "implicit social graphs" -- social graphs that get built for us rather than by us -- definitely worth reading.

Anyway, so much of what I see each day on Twitter is wasteful: boring personal messages, links to sites I'm not going to click on, self promotion, etc. But I keep checking it reguarly because every few days I find a gem -- a piece of information or an insight that makes me laugh out loud, makes me more informed or smarter or causes me to look at things differently. I love when that happens.

I realize different people use Twitter for different reasons so they're free to Tweet whatever they feel like Tweeting. But over the last two years I've noticed that the best Tweets, the Tweets that are really valuable, seem to have these four things in common:

No web links; all of the information is communicated in less than 140 characters
No hashtags (#), they're annoying, unless they're added to make the Tweet funny, which can work sometimes -- see @bronxzoocobra
No @s, unless it's a Retweet; generally conversations on Twitter are lame
They aren't a simple statement of what someone is doing or where someone is; e.g. "mowing the lawn" or "at the movies"

To do this well you actually have to think pretty hard, you have to initiate, you have to create. That's why these kinds of Tweets are the best, and probably why they're so rare.