I've had an iPhone since before MobileMe (iCloud's predecessor) and have used the notes app on the iPhone. Back in iOS 3.x, the notes were associated with an email account and synced to the mail app on the Mac. With MobileMe, and and now iCloud, only notes created using the "cloud" account would sync across iOS devices. This wasn't a big deal until today, when I (finally) purchased an iPad. I'd like my notes to sync wirelessly between devices, but since the notes were created from a non-iCloud account, they won't snyc. There's a simple solution: Copy and paste all notes at once from "On My Mac" to "iCloud".
Here's how (this assumes that you've snyced your notes from your iPhone to a Mac): Open the Mail app on the Mac. Click the little arrow after Notes. I have two options: "On My Mac", and "iCloud". Click "On My Mac". Click Edit --> Select All (Command A) then click Edit --> Copy (Command C). Click "iCloud". Click Edit --> Paste. Your notes are now copied from "On My Mac" to "iCloud" and will sync if your turn than option on in all iOS devices. What's even better, is that any change made to an iCloud note on the Mac syncs with iOS devices even though on Lion OS.