I still nip into Gmail quite regularly, especially when I'm already in the browser or a tab is already open, but if I'm sitting at the desktop and need to compose an e-mail, at some point the default returned to alt-tabbing to Thunderbird.
No waiting around, no messing, blank e-mail window up on the screen as fast as I can hit CTRL+N.
Back when everyone switched to Gmail circa 2005ish, hitting CTRL+N quite probably meant a firestorm of random IO hitting a magnetic disk, on a machine with barely any RAM for cache. The equation has long since changed, and your reason to use Gmail might now be your reason to use a desktop client. Highly recommend giving it a shot