wisdump has a recent post asking which resolution designers will be aiming at during 2007.
I run a fansite for a popular MMOG that has a game is not very expensive in processing power but has a minimum resolution of 1024x768. This site I run received from 05/12/2006 and 05/01/2007 about 440 visits. From these 440 visits only 2.73%(12) visits were under 1024x768, 46.14(203) were 1024x768. Although the population would by nature be using screen resolutions over 1024x768 the numbers are quite clear that even in this segment lower screen resolutions should be considered.
I my self will not be designing for anything bigger then 800x600. Also if the surfer has a screen resolution of 1024x768 he/she might use a sidebar for history or bookmarks or even browse the web using only part of the screen for the browser (multithreading). These behaviors will reduce the available screen area for the website drastically, making sites designed for anything over 800x600 look too BIG and hard to read.
Also, the future doesn’t seem to bring much bigger areas for designers to work. I would like my sites to be readily viewable in a PSP or some other hand held, and those don’t seem to be getting over 800x600.