What about SMS users? The 140 character limitation is there for them. It would fragment the service for them as they would only be able to receive short tweets or receive tweets split into multiple messages.
Whereas I'm not saying they should remove the limitation, I think that should be the last of Twitter's concerns. Not sure if there's any official numbers on this, but I'd guess the percentage of tweets sent by SMS is not much more than 3 or 4%. It's what made Twitter big, but texting tweets is legacy now.
