I hate the idea of being notified of each individual message. Considering how often it's an automated e-mail or somebody copying me in to something rather than something actually useful... well, for my use of e-mail it's a pointless distraction.

Still, I wouldn't mind having the unread count on my iPhone's Mail icon be accurate, instead of a half-hour out of date. I'll probably enable this sometime soon and continue to leave new mail notifications off.