I've written several times over the years about the need for Notes to sync automatically between the iPhone and the Mac Mail.app Desktop application. Well, unbeknownst to me (because I stopped using Notes in Mail.app because of the lack of this feature), in iOS 4.0 Apple has built this in.
I didn't test it right away when the release came out, and just now that I haven't written about it either since they built this in. But it works.
If you have an IMAP account, you can go into your account settings on your iPhone and turn on "Notes" in that account's preferences. Mail will create a folder called "Notes" on the IMAP server, and your "Notes" on Mail.app will be sync'ed Over-the-Air with your iPhone.
I have my Mail.app set up like this:
So that all my notes and to-do's stay intact in one account, and not spread apart different accounts. But there is more than one advantage to MobileMe for this particular feature. If you set it to MobileMe, Notes are pushed. (As opposed to pull, as they would be with other IMAP accounts.)
In short, Apple enabled Notes syncing in iOS 4.0. It works. Give it a shot.