Bogie,
 
I think 1024 is a safe choice for the web.  Initially, I was surprised that the NY Times web size was 800 or so, but they have switched to 1024, which should be a barometer for the way "the masses" view the web.  In addition, I think Photoshop CS3 requires a minimum screen size of 1024 x 768.  It's hard to believe that many people run 800 x 600 these days.