We recently tried to migrate from a Windows 2008/Exchange 2007 server to a OSX Snow Leopard Server box... what a nightmare!
Setting up all the mail accounts was strange, because you set up a primary email account username (let's say the username is bob for the email address bob@robert.com). Then you can add aliases for that account, like robert and rob. The weirdness comes into play when sometimes while adding aliases, for no reason, an alias name will take over as the primary account name (the primary account name will change from bob to robert). The only way to fix this is to REMOVE THE ACCOUNT, or to keep adding random aliases and removing them in hopes that the real account name will flop back to primary. This is all a known issue on Apple's support site.
The easiest part was moving mail (we just set up connections to the old exchange server and the new mac mail server, and dragged over the folders from one to the other, worked like a charm.)
Calendar export import was iffy, but eventually worked.
Contacts? Terrible. We copied our contacts over from Exchange to Mac Server. The Mac Server contacts format is CardDAV, a new standard for storing contact information. This would be OK if all of our iPhones support CardDAV (they don't!).
With Exchange, our iPhones synchronized flawlessly using Push for email/contacts/calendar events. Since iPhone doesn't support CardDAV, the only solution to get your contacts onto the iPhone is to set up Mac address book on a desktop machine to connect to the Mac Server. Then, YOU HAVE TO COPY ALL OF YOUR CONTACTS TO YOUR LOCAL MACHINE. Now you have two copies of all your contacts, one on the server, one locally. You can then tether your iPhone and sync the contacts with iTunes (iTunes won't sych contacts on the server, which is why you have to make a local copy of all the contacts). Any time you have a new contact on the server you will need to put it on your local machine as well.
So if that wasn't bad enough, here's the next fun thing: OS X SNOW LEOPARD SERVER DOES NOT SUPPORT PUSH EMAIL TO IPHONES (despite their site saying it does!). This was a big WTF moment for us, considering these are both Apple products.
Finally, we had a ton of problems with sending Calendar invitations -- these would (seemingly randomly) attach themselves to the wrong Calendars. Sometimes the event would attach to a local calendar, others to the calendar on the server. The only solution we found to this was to DELETE local calendars. /sigh
Eventually we just sent the server back, Apple was kind enough to issue a full refund without a restocking fee. We moved everything back to Exchange. :(
