This happened to me today – a new note I created on my iPhone would no longer turn up in Outlook after a sync via iTunes (PC/laptop based). It seems to have been an issue after upgrading the iPhone OS to v4 (at least I certainly didn’t have the problem before I updated the iPhone version – but then the last time I created a new note directly on the iPhone (as opposed to editing) was pre-v4, so it could have been coincidental. Still, moving onward…).
I searched for a solution on the web, but couldn’t find anything much beyond the usual “un-tick and tick again” suggestions. Not much help so far (so normal when it comes to trying to find how-to data and help from Apple, still…).
THEN, I noticed that Notes on the iPhone has “accounts” – i.e. go into the Notes app and tap “Accounts” – and I saw 3 separate Notes lists: All Notes, From my PC, and myemailaddress. We’ll ignore the last, because there’s nothing in there.
To cut a long solution short… if you create a new note under All Notes, it doesn’t seem to sync with Outlook via iTunes; BUT if you tap on (i.e. use) From My PC, any notes you create in there will now sync with Outlook (and vice versa). Fixed!
Incidentally, you will see the new note(s) under All Notes, but basically I’m not going in there again if I want it all to keep working.