I've been using MobileMe to keep some things, including calendar, in sync between my work's iMac, my macbook and my iPhone for over a year. Generally I've been pleased, but after upgrading my phone to 3.1 and my iMac to Snow Leopard I've encountered a very irritating problem where my "accounts" in the calendar on my phone had duplicated and seemed to spawn multiple constant synchronization threads, to the detriment of my using the phone or having the battery not drain. After screwing around with it today and finally getting some live chat help from the MobileMe support site I figured out how to clean it up and what is causing it. First the cause is the subscribed calendars I have on my desktop iCal. I have one calendar, but I subscribed to a handful of other calendars so I could quickly look at what a few other persons of interest were up to. I've had it this way a long time, but it was just during the last few days I noticed I could see the subscribed calendars on my iPhone. And then everything went wrong, and for every one subscribed calendar I had I ended up with a new calendar account.
The fix was found partially through reading this article the MobileMe support chat rep sent me, iPhone/iPod touch: Resolving duplicates and removing all contacts/calendars/bookmarks with MobileMe or Microsoft Exchange ActiveSync, and having the problem resurface once I had "fixed" it once.
First turn off "Push" on my phone, then in iCal remove all subscribed calendars and sync it to MobileMe, this is only a minor annoyance for me as they are all google calendars and I can view them in that interface. And then on the phone toggle the calendar sync setting for the MobileMe account from on to off selecting to "delete" the calendar data from the phone each time, until finally left with a single account.
If I knew an easy way to report this bug to Apple I would, but I wasted enough time on it now and don't want to go hunting for a way to tell them.