I usually squizz through SO by opening the frontpage, then right-clicking on the questions I find interesting or want to help answering and open them in a new tab.
When I open SO in IE7 and do as described above, the page stops responding to PgDn. It works when it first loads, then stops working when a new tab is loaded in the background. If I hit the scrollbar once, it's responsive again. It's been like this for a while.
Even though this is not a major issue, it's still something that someone should look into.