Before 10.5.6, having MobileMe set to automatic syncing usually meant much grief. The syncing process was slow and the entire computer would slow to a crawl.
As of 10.5.6, if you change data of a Address Book record, the sync starts almost instantly and lasts for only a few seconds. Within 30 seconds, the change is on the iPhone.
Very nice!
Because of the awful syncing performance, I had changed MobileMe to only sync Address Book, Bookmarks and Calendars.
I’ll report any issues I find!