Now and then, while I am reading a thread on the forum, I find the PgUp and PgDn keys don't work in IE 7 on Vista SP1.
I can re-create this by clicking in the body of a reply (below the heading). Once clicked, all the page navigation keys stop working.
To restore navigation, I can click in the reply heading or to the right of the thread.
Scrolling using my Thinkpad Trackpoint device (superb!) is also rather clunky, which is why I sometimes resort to using the keyboard...