Brian Chappell over at MarketingPilgrim has a list of 75 or so internet marketing professionals actively using Twitter. If you’re new or old to Twitter this is a nice resource:
Many underground conversations go on within Twitter that never make it to the blogosphere or news sites. It can be a dynamite location for link bait ideas, breaking stories, and general topics you might not think about on a daily basis. You might even find yourself obtaining clientèle through it. I really could go on and on with what you could do with Twitter.
As an aside, over on my personal blog (?), I made some remarks about how Twitter has changed since the “good old days.”