I run at 1280X1024, and I know a lot of others who do as well. Here's some info I dug up:
"The two most popular screen resolutions...
800x600 - 47%
1024x768 - 46%
You should typically design for the lowest common denominator. In this case it is 800x600. This doesn't mean that you can design 800 pixels wide. I normally recommend that you not exceed 760 pixels in width as you have to account for scrollbars and the like.
In a perfect world, you should design the site so it is fluid with 760 pixels being your absolute minimum width. This way those who are using higher resolutions will get a site that fluidly fills their browser window. It is a tough design environment to work in, but it can be done.
If you do go with a fixed width, no more that 760 pixels and you'll be able to appease at least 93% of your audience. If you have visitors that are still using 640x480, they will get a horizontal scrollbar as they probably do with 90% of the other sites they visit.
I'd definitely target the 800x600 resolution."
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Mark Martinez
University of Florida