ergophobe - 9:16 pm on Feb 21, 2011 (gmt 0)
With due consideration of lammert's concerns as well as some usability concerns, I tried GMail. I'm still a bit weirded out by Google having all me email, but once you get used to having really high-quality search integrated into your email, it's hard to give it up.
I don't know what GMail Pro is, but I do use Google Apps GMail as well as the regular one. As far as I can see, they are fundamentally the same in terms of usage.