Neither .2 nor iOS6 upgrades fixed my problem. Genius Bar was stumped, too, saying they had never seen this problem. My next stop is tech support to ask for an iCloud acct reset; saw this worked for Lion6Alpha (his post below).
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I FINALLY have this problem solved. It took, I don't know, almost three months of near-endless e-mails and calls with tech support but now I can synch everything everywhere.
The solution? Get the engineers to reset your account. And keep making them reset it until it finally takes.
I get the feeling the main problem is not that iCloud doesn't synch right but that when it does, it's a glitch inside the user's account and no one wants to just do the immediate and obvious thing: Reset the account. Once they finally did this, everything worked and still works across both Macs, my iPad, and my iPhone.
So, my suggestion is get in touch with tech support AND DO NOT LET THEM DROP YOU. KEEP BUGGING THEM UNTIL THEY BUG THE ENGINEERS.
Now that it's working I'm actually very pleased with iCloud as a transportation device.