1280x1024 on this monitor, 1600x1200 on my workstation monitor, 1280x800 on my laptop, and 1280x1024 at work.
I think it is generally good practice to design for 1024x768 or at most 1280x1024. This is not only because the majority of people still do not use higher than 1280x1024, but also because many people do not necessarily browse with their web browser "maximized" or full-screen. This is a surprise to me as I hate not having my browser maximized, but apparently this is common.
Additionally, even if everyone did have wide screen monitors, the reality is that the most comfortable reading and information review format for people is shorter (width) blocks of text, with vertical scrolling. This is due to the need to move our eyes a certain distance to read, and the limitations of peripheral vision. No one wants to have to turn their head to read! And if your eyes continually have to traverse a greater horizontal distance when reading, you will experience eye fatigue and discomfort more quickly. This is not necessarily a consciously recognized issue of course, but in practical use you can quickly see how much people favor less wide screen information presentation. Movies and TV, on the other hand, are interesting in wide screen because we do not need exact identification of all screen elements, and engating our peripheral vision is more immersive. Most web pages are not aiming for "immersion" and so it's a bad idea to try to take advantage of all screen real estate of a wide screen monitor.
That's my 2 (or 3, or 4...) cents...
- Oshyan