When I look at my banner stats, the 700 X 80 or 600 X 100 banners pull significantly better than the 468 / 480 ish banners do. I run 1600X1200 (20 inch screen) and I can tell you that standard 480 banners look positively tiny now.
http://www.thecounter.com/stats/2005/December/res.php
These stats show that larger than 800x600 is now 70%... another blog I looked at suggested that number to be closer to 80 -90%. I don't think it is at that level yet, but every day that goes by means another 14 inch monitor is retired and replaced with a 17 inch flat panel at 1000 X 700 or more (1024 X 768, I think is the next step up the ladder).
The size of the viewing window will change the effectiveness of your advertising, so regular old banner ads might not be your best choice anymore.
Alex