I must admit I didn't sign up yet - just read the homepage - but something that would be super useful on such a system is throttling tweets. I've seen more than a few instances where an employee screws up or goes 'rogue' and either goes off on a rant or posts the same thing over and over. It'd be great to only allow employees to post, say, once per hour or whatever, so any problems could be contained.
Or perhaps an employee kill switch that deletes every tweet they've made in the last user-defined number of hours?
-- Pete, founder, Pixie Labs