My work laptop, when I’m at work is usually connected to an external CRT monitor which runs at 1280×1024. Due to some really annoying bug in XFree86, it wouldn’t display any screensavers at the full screensize. Instead it would run the screensaver at the resolution of the LCD panel in the laptop (which in the case of my laptop was 1024×768). So today at lunchtime I finally had enough, and after a bit of googling I found the solution on JWZ’s website (the author of Xscreensaver). To fix the problem, edit ~/.xscreensaver and put in the rather appropriate GetViewPortIsFullOfLies:True at the bottom of the file (or just set GetViewPortIsFullOfLies to True if its already there).