I've said it before, but the iPhone and Leopard were supposed to come out together. That's why we have functionality orphans like Mail and Notes.
Write handy notes you can access from anywhere — including graphics, colored text, and attachments. Group notes into folders or create Smart Mailboxes that automatically group them. Your notes folder acts like an email mailbox, so you can retrieve notes from any Mac or PC or access them from your iPhone.
There's a little blurb about To-Dos as well. They're getting integrated into the mail client. Hmmm... it would make sense why the Calendar application doesn't have to-do items, if Apple has been planning to put them into their Mail application. This functionality would make Apple's Mail.app a lot more like Outlook, which I think most people will welcome.
Create to-do items directly from email messages or notes in Mail. Simply highlight text in an email, then click the To Do button to create a to-do from a message.
I don't think it's long before we get a Leopard patch for the iPhone. I'd imagine that an iTunes update will accompany it as well, unless the functionality to sync to-dos and Notes is already hidden within the current version of iTunes. There may be other hidden iPhone updates as well; rest assured that I'll post as soon as I read about them.