Follow up to my earlier post. It appears that the notes that "disappeared" from my iPhone fit in a certain date range. Seems to be June and July. A note I created in August didn't disappear. So I just emailed the notes from June and July to myself. I created new notes on my iPhone in the Notes app for my Yahoo account. Automagically they appeared in my Yahoo folder and didn't disappear from my iPhone when I synced again. Solution?