– You can’t turn on push services on the iPhone without being forced to also use your me.com email address on your iPhone. So if you’re one of the many people who still wants to use your mac.com email address (instead of me.com) AND use push services, you’ll end up with double incoming emails on your iPhone — one email message into your mac.com email account, and one email message into your me.com email account. As soon as you turn on push services on your iPhone, the iPhone AUTOMATICALLY adds the me.com email account into your iPhone’s mail program. There is no way to turn off the me.com email account while still receiving push services on your iPhone, so unless you like receiving double email notification, you have to choose between EITHER using your mac.com email address OR using push services on your iPhone.

– The colors that you’ve assigned to your calendars will sync between your Mac and the MobileMe website, but they will not appear on the iPhone. In fact, you have NO WAY AT ALL to specify calendar colors on your iPhone. And on the MobileMe website, you can’t change the calendar colors to anything except a small amount of predefined colors (no custom colors).

– Custom fields that you’ve created in your Address Book will appear on your Mac and the MobileMe website, but NOT on the iPhone! That’s bad enough. But it gets even more confusing, because the custom fields will appear on the MobileMe website only for contacts whom you’ve already assigned data to those custom fields on your Mac. There is no way to make those custom fields appear on the MobileMe Contacts website. They don’t appear by default like they do on your Mac, and there’s NO WAY TO EVEN MANUALLY ADD those custom fields to the MobileMe website.

– To do’s will appear on your Mac, but they do NOT appear on the iPhone, and they only recently appeared on the MobileMe website. But the big problem on the MobileMe website is that the preference to “hide to do items with due dates *AFTER* the calendar view” is gone. It has been replaced on the MobileMe website with a preference to “hide to do items with due dates *OUTSIDE* the calendar view”. This is a big problem for viewing overdue to-do’s on the MobileMe website, because you can’t view overdue to-do’s whose due date was BEFORE the CURRENT CALENDAR VIEW. At least in iCal, overdue to-do’s are still visible, no matter what your current calendar view is. In other words, overdue to-do’s “carry forward”. But on the MobileMe website, overdue to-do’s will DISAPPEAR (as if you’ve completed them) if their original due date is not in the current calendar view that you’re looking at. (Also, on a minor note, the to-do pane disappears every time you log out & log back in to the MobileMe website.)

– SUBSCRIBED CALENDARS DON’T APPEAR on the MobileMe website NOR the iPhone! What good is it to subscribe to the US Holiday calendar and the Jewish Holiday calendar and all of those sports calendars… if they don’t appear anywhere but the Mac?! Yes, we know there’s a workaround for exporting your subscribed calendar data and then importing it in as a regular calendar… but that defeats the purpose of having a subscribed calendar to begin with!

– Custom ringtones from the iPhone can sporadically disappear when syncing your iPhone to your Address Book. I have to play with this some more to nail down when this happens, but I think it happens after making a change to a contact on your iPhone or Address Book that has a custom ringtone attached to it, and then syncing. The MobileMe website and the Address Book on the Mac have no capability to hold a field for custom ringtone, so it seems to just “lose” this information.