1024*768 is alot more comman now and is what the majority of people use but it's so easy to keep a site within the 800*600 and as there are still people using that resolution it's easy enough to accomodate them in my opinion

Check your site stats if no one (or practically) no one visitng your site is using 800*600 then by all means make it 1024 wide but if there are still people using 800*600 then don't cut them out.