I just performed the iPhone Update (to version 1.01) and it went without a hitch. There appear to be numerous small improvements but nothing to get too terribly excited about. Overall performance is just fine (WiFi feels a bit snappier, EDGE about the same) and the only thing I needed to reset was the password on my WiFi connection. Others who have hacked their iPhone are reporting that a full restore needs to be performed and mail accounts and other settings reset. Jason O'Grady has the details here. More anecdotal information is available from the TUAW team who are "live blogging" the update. An updated iPhone manual is also available from the Apple web site (link is in the updater startup screen).