From the guys over at Panic, who handle all support tweets via e-mail using a self-built solution named Burnside which bridges the gap between Twitter and e-mail:
Tweets go into a regular mailbox. When we reply, they go back out as tweets. Since multiple people can work out of the same IMAP box, it’s fast and efficient. And as an added bonus, as we archive tweets one by one, we’re building our own searchable index of tweets in Mail.