I have listened to many iPhone podcasts and read both Pogue and Kelby’s iPhone books (and Apple’s own user manual) and I don’t think I have heard or read any mention of the following scrolling tip when using Safari on the iPhone. Perhaps this behavior (gesture?) was added in a recent update.
Anyway . . . while browsing a website (in portrait or landscape) double tap near the top of the page to scroll up (seems to move about a 1/3 to 1/2 screen) and double tap near the bottom of the page to scroll down the same distance. I seem to be able to find my place to continue reading better using this scrolling technique than the more common flicking.
As has been pointed out, if you double tap on the bar with the clock at the top of the page, you will scroll to the very top of the page. John