Well, it sucks for the people trying to sell followers. They have to make a new account everytime they want to follow someone because all of the other ones get deleted every month it looks like.
If you get banned for no apparent reason if you're not a spammer just send them an e-mail to reactivate your account. It usually takes about 24 hours for them to review and activate.
Twitter should start validating accounts better! Use the good ol text message or phone verification system. If someone doesn't validate then their actions are limited. Unvalidated accounts can't: Mass follow mass DM Mass reply customize background
Plus ca change - today I blocked about 15 followers offering to show 'hot pics'. I think it's a real problem for twitter - as soon as they ban 1000, 10000 new ones pop up, it must be eating up resources, they need to do SOMETHING to get a grip on it.