As said in previous posts (you might want to do a search), Notes as of right now are not part of MobileMe, but part of iTunes syncing.
So, the next time you have your iPhone/iPod Touch docked (or connected), go to your iPhone/iPod Touch in iTunes and in one of the settings screens you'll see a check box to enable Notes syncing.
Notes will be synced both in the iPhone/iPod Touch and in Mail where Notes are now located. Just remember that syncing is not done over the air, you must dock/connect your iPhone/iPod Touch to iTunes in order to sync (a la original methodology).