I used to use that width on my old forums but I like it like the width of the default skin now as most users are upgrading their old monitors to better widths now. That width was excellent when everyone was stuck at 800x600 but as cheap as LCDs have gotten, widescreens are getting more common.
Well, don't forget about all these new mobile Internet devices (iPhone, eee PC) - I think keeping it well readable on displays with 800 px width is a good idea.