The breakdown of screen resolutions among visitors was as follows:

640x480 and below 0.5%
800x600 19%
1024x768 59%
1280x1024 18%
1600x1200 and above 3.5%

Similar figures from a broader range of sources can be found on Chuck Upsdell's Browser News web site.
While 1024x768 is clearly the dominant screen resolution, 800x600 is still a very significant screen size; the technical nature of our web site probably skews the results in favor of larger screens. Any web site design that looks bad at 800x600 is not a good design. Web sites should also take into account the very small screen sizes of handheld devices and the needs of blind users using speech-enabled browsers; a well-designed web site is still useful even when the browser lacks support for "eye candy."