Now that Mail in Leopard features Notes, iPhone users are (im)patiently waiting for an iPhone update that actually syncs with these notes. In the meantime, heres a work around:

The Notes in Leopard will are really just specially formatted email messages. That being the case if you have an IMAP based email account such as .Mac you can assign your notes that you create in Mail to your .Mac (or other IMAP account) by simply expanding the Notes area and dragging the notes to the appropriate IMAP account.

Once you do this and go to your iPhone the "Notes" folder will be there in your email folders and you'll see the notes you created on your Mac.

While this doesn't use the iPhone's Notes app and it's only one way for now (Mac to iPhone), it's better than nothing and it allows you to get long formatted notes onto your iPhone that don't have to be typed in on the iPhone's keyboard. Also if you update the note on the Mac it will be updated on your iPhone as well.