After setting up Mountain Lion on my Mac, I went and tried the new Notes sync feature. I've been syncing my notes from my iphone to Gmail for months now (or so I had thought).
But going into the Notes app on my Mac I did not see anything newer than 6-8 months ago.
Then I checked gmail and the Notes label showed the same. And a few google searches turned up empty.
The fix for me was to go into iPhone settings > Mail, Contacts, Calendars > Fetch New Data > Advanced > and change my Gmail Notes account from Fetch to Manual.
Then I relaunched the Notes app on my phone and everything magically synced.
Scary thing is I think none of my Notes were backed up, even though I thought they were.... Hopefully this will help someone else out there.