Apple's never been so great with sync. Nonetheless, the idea of MobileMe is great. In practice it just doesn't work so well when you have data flowing through multiple devices. Here's how to fix MobileMe when it inevitably screws up.
Photo by Ian B. Line
MacLife's posted a great guide on curing your MobileMe woes that can basically be summarised in three words: reset, reset, reset. When you're syncing with a bunch of devices, MobileMe will often have trouble deciding what data to delete and what to keep. In my experience, it errs on the side of keeping everything and so no matter how many times you delete address book contacts, widgets or whatever, you find them popping back up again. This is extremely frustrating after spiritually cleansing your data.
The tutorial explains that there are a bunch of places you need to reset your data. First, the MobileMe preference pane in System Preferences is where you want to start, but you also might not be aware (I wasn't) that you want to reset syncing data in iSync as well. If you're syncing to an iOS device, you should also reset sync data on the phone (in Settings —> General —> Reset). Once you've accomplished your great reset adventure, you'll need to designate one computer to make the first sync. (If you only have one computer, congratulations! This is easy!) Once your primary computer has synced up its data, you can start syncing everything else. Be sure, when asked, to "Replace Data on This Computer" so you're pulling in all the data you just pushed to MobileMe and not contributing to a new mess that you'll just have to reset again.
While not using MobileMe is probably the best cure for frustration, it is nice in theory and sync is not exactly an easy thing to accomplish. Hopefully MobileMe will continue to improve. For now, a lot of resetting can help you out when MobileMe doesn't feel like working properly.