Hey, all! Several people from 2.5 Men are on Twitter, some tweeting more than others. I'll keep a running list here, adding people as they join.
Ashton Kutcher (Walden) @aplusk - one of the oldest and best accounts
Jon Cryer (Alan) @MrJonCryer - often tweets about whether his character suffers any indignities in upcoming episodes
Charlie Sheen (Charlie) @charliesheen - You can't be #winning if you don't follow him!
Holland Taylor (Evelyn) @HollandTaylor - unfortunately mostly retweets and responses, with some proverbs tossed in
Lee Aronsohn (co-creator/writer) @Benny Ace - random, sometimes humorous tweets
I'll add more as others get created and verified.
Also, as of 2/2012, any account on Twitter or Facebook claiming to be Chuck Lorre is fake; he even dedicated his 2/16/2012 vanity card (#378) to the subject, so don't expect that to change soon.