I love me some Fallout 3. In fact, it's paused as I write this.
That said, there's a fairly well-known bug (definitely in the Xbox version, I don't know about the others) where the PIP-Boy display shifts up occasionally, and eventually (if you access your PIP-Boy enough) the top portion is off the display, rendering the top line of information (say, your HP and weight carried) invisible.
Is there a fix for this aside from quitting and restarting the game?