I've seen quite a number of MobileMe sync problems over the last couple of months. Some items that I add/delete/modify in my calendar don't make the jump between laptop and desktop, or vice versa. It's completely intermittent and always works perfectly if I deliberately try to catch it out. This is extremely unhelpful of it, as it means I just can't trust my calendar on either machine to be correct.

 

I've found a way to at least get things back in sync (as far as I can tell without doing an exhaustive comparison) though it remains to be seen whether it will actually stop things going wrong again. On all machines, open the iSync application, open its Preferences, then click the "Reset sync history…" button, and select "Merge" when asked. It might ask several times, for various types of sync data, with big spinny-arrow pauses in-between. You're putting yourself in the hands of MobileMe's sync algorithms here, so don't come crying to me if it makes your kettle fur up with scale and your cat leave home. I'll update this post as and when I determine if the more general problem is licked. Sadly my gut feeling is that it's too much to hope.

Update: Still been having problems and have been tearing my hair out. The recent OS X 10.5.7 update promises some sync improvements though isn't specific about what. I'm hopeful, but I won't know for a couple of months as it usually picks just one or two important items to not sync every now and then. Enough to keep me on my toes.