I'm at 1024 x 768. I know my mom and brother use 800 x 600, so websites are better designed for that resolution since a lot of people (buyers of stuff!) still use it. My website squeaks over in width, so on their screens, you have to scroll to see it all. Most sites work fine at either resolution. Tables are the big thing to watch on width for.
Another thing to watch for is a lot of people are now using Mozilla. I have 12% of my last thousand visitors using that. I had to rewrite all my pages to get them to work correctly for Mozilla. It's a free download, so it's easy to test a site. Small changes from Explorer really messed with placement of things. My header didn't post correctly on every single page. I also have some pictures that rely on mouse over alt text descriptions that don't work in Mozilla. I'll need to come up with a different way of doing those.