The latest version on iTunes 8.2 prerelease contains a Notes syncing pane. But you'll need 10.5.7 to use the functionality. So we are going to hazard a guess that 10.5.7 is going to have a Notes updateand is probably coming fairly soon.
Update: It was working (buggily) for iTunes 8.1 + iPhone 3.0Beta 3 in 10.5.6 and broke in iTunes 8.2b + iPhone 3.0B4
