You might be a hardcore Twitter user if:
- you look at 2000 followers as "getting started"
- you think 5,000 tweets was a long time ago
- you’ve ever tweeted with people in the same room as you (conferences don’t count)
- you’ve considered unfollowing your partner because "they don’t post enough useful stuff"
- you’ve ever spent 24 consecutive hours tweeting
- you’ve ever tweeted BEFORE calling 911 when witnessing an emergency
- you use 4 or more different twitter clients on the same computer
- you’ve tweeted while: parachuting, swimming, skating, spelunking, etc…
- you recognize when someone is back to Twitter, because "hey, that person is tweeting again!"
- you miss your Twitter friends after an hour offline
- you’ve ever attended multiple Tweet-ups in the same week
- your Twitter withdrawal symptoms, on those rare occasions when they do happen, only take a few minutes to appear
- you post a question on Twitter and get 500 responses within minutes in 3 different languages
- you think the definitions on the sidebar of Twitter.com looked better at the top of the column rather than the bottom, and you tweet about your opinion
- you’ve ever written your own Twitter client because the ones you use "don’t work right."
- you automatically add hashtags to everything you say in real life (at least in your head)
Please add some more ideas in the comments below and I’ll incorporate them into this list.