I decided to take the big jump from using an ASP Exchange Service to Apple's MobileMe Service. In March we made the switch over and I would say it is pretty cool, but I am definitely not a "raving fan".
First the good. MobileMe does a good job of syncing between PC's and Macs. We have ran into a little problem here, but all in all it does a good job. I also like the way it syncs the Safari favorites. Since the new beta came out, I use Safari on both my Macs and my PCs. I do this with Foxfire using Foxmarks. It also has a very slick Web UI, even if it is dog slow. I assume they are going to fix that, but right now it is really frustrating.
Now the bad. If your use to Exchange, you will find it very bad to go back to a standard IMAP server. I had forgot how much value having Indexed Views and great Offline Access gave me. The folders on MobileMe on occasion sync to my client, but I never have all of them. This is very unpredictable. Also, when you delete a message it crosses it out, but only removes it from the view when you change folders (This is in Outlook, but Mac Mail does the right thing).
The price difference between MobileMe ($99 per year) and an ASP Exchange Server ($50 per user per month) is the main reason we made the switch. I hope the MobileMe team focuses hard on the IMAP capabilities and specifically its integration with Outlook. Fingers crossed!