According to 9to5Mac the next release of Lepoard 10.5.7 and the new iTunes 8.2 will be adding this functionality.
I hope so because syncing Notes was my very first thing that i’ve missed on the iPhone software.
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 update…and 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