I liked this because Mail then kept all of my mail synchronized locally. If I unplugged for a bit and needed to grab a message, most of my mail was current and I could get to it. I still use Safari and the Gmail interface to create and generally read my messages though.
The problem is Google's implementation of IMAP apparently leaves much to be desired. What I found in Mail was that if I sent it from Mail a new label was created in Gmail called Sent Messages. I didn't really like that. In addition the Junk Email filter in Mail was getting false-positives on some of my e-mail, and a new label called Junk Email was created in my Gmail account; Mail would move what it considered junk into that label.
So, in the end it has become a little painful. Not too bad mind you, but enough to make me look around. What I really wanted was near instant notification of a new message arriving in my Gmail account.
I had already been using Gmail Notifier on my Windows XP machine and found it quite handy. Sure enough Google had a Mac version when I checked so I figured I'd give it a spin.
I won't go into too much detail talking about it because this little video does a great job walking you through it:
I've now put Mail on the back burner and am using this to keep track of not only my e-mails but also my upcoming calendar events. It's pretty cool.