The Home and End keys take you to the top of the page/document/whatever. I think pgup and pgdn skip forward and backward one page (as opposed to one screenfull). There are many, many sites on the web wondering what on earth they are for.
The only application I use them for is Terminal for scrolling through the history, and I press shift-pgup/pgdn to send a PC-style page up and down to the *nix applications underneath (e.g. going up a screenful in mutt on my macbook is shift-fn-up arrow, or shift-pgup on the external keyboard).
In every thing else, I use the command-arrow shortcuts to jump about quite happily. Thanks to the fact that there are no separate home/end/pgup/pgdn keys on the macbook, I have got quite used to command-arrow instead of reaching up for the other block of keys, so all is good.