You know how when you hit "Get Mail," you get one of two sounds? One indicates you have new mail, the other that you don't.
Lately, using POP Gmail, I'll hit Get Mail, it'll make the "no new mail" sound, then proceed to sync, and grab my messages. If I have mail or not, it makes no more sounds. However, if mail itself does the checking (that is, I don't tell it to get mail,) the sounds work correctly.
Just thought I'd mention it.