As per Job's Keynote address, the iPhone will sync with your Mac (or PC) via iTunes. He said it will automatically pick up all your e-mail accounts and web bookmarks as well as your music and video (of course).
Syncing via the internet was never mentioned, but given that the phone/browsing battery life is estimated at 6 hours, and this thing's going to be hard to put down for the first few weeks at least, I suspect we'll all be dropping it in the cradle on a regular basis.