Same here. If I'm away from my computer, I use GMail, but if I'm at my computer (i.e. most of the time), it's Mac Mail. Why pass up the UI superiority and integration with the rest of the system? Using both doesn't diminish my ability to use GMail on the road, which is where it has the obvious advantage.
Yeah, but it means you're on the hook if things break. I switched to Gmail a few years ago, and I love that any Gmail breakage is Google's problem, not mine.
Gmail is great, but why would you ever rely on a 3rd party for a main form of business communication? I like having my own servers, but I build in lots of redundancy, so that I'm covered. No matter what happens.