I've been a big fan of Google Apps since I setup my first domain (this one), almost 2 years ago. It's dead simple to setup, you get most of the features of a GMail account with the benefit of having your own domain name, they recently added Microsoft Exchange compatibility, and it's free (if you can squeeze all your emails in ~7GB).
We recently migrated one of our domains from Exchange to Google Apps and encountered an unexpected problem. When forwarding email from an account on one Google App domain (the secondary account) to an account on another (the primary account) the emails would automatically get marked as read and then skip the inbox in the primary account, effectively never showing up on my radar. Not very convenient if you're like me and you live in your inbox.
As a last resort I could have setup my primary account to poll the secondary account for new emails via POP3, but I figured I'd try one last thing before implementing that hack. I logged my secondary account and turned off the forwarding in the "Forwarding and POP/IMAP" tab, then setup a new filter that would forward email that showed up for "*@secondarydomain.com" to "email@example.com". Problem solved.