File this in the "I can't believe I haven't done this before" box. I've done it now though. Finally. I've moved my email to a hosted exchange provider. It was simple; far simpler than I'd have imagined.
I set up the service - I use Sherweb - in about 20 minutes across 3 Macs and an iPhone. That didn't include the time to install Office 2008 on one of the Macs - so add 30 minutes or so for doing that if you haven't already done it.
Moving my email from the hard drive of my MacBook Air was as simple as selecting a huge set of it, dragging it and dropping it into my server-based inbox. I had my calendar in iCal so I synced it to the Exchange server and that was done. Contents, from Address Book, ditto.
So if I move Macs later, or even move back to a PC, I guess I'll never have to go through the whole conversion process again, unless I manage to find something that doesn't support exchange - and I really can't see myself doing that anytime soon.
What are the flaws? I haven't found any so far. It just works. That has to be a good sign given if anyone could have found a way to break it, it would have been me.