Since users are working using the various apps tabs on the left side of the screen, and emails are being received while using other apps, wouldn't it be awesome to have the number of new emails to show up next to the Mail icon?  I know we have the little sticky pop up thing at the bottom right, but not all of us will click on mail as soon as we get that notice.  Mails may build up before we check, but with an indicator of how may new ones, at least we know how many it's been since we checked.

This "badge" feature is something that users of Mac OSX often benefit from while using Leopard Mail or instant messenger functions.