I've heard that screen resolution is important because not everyone uses the same.
How reliable is the tool and are there any statistics on screen reolustion use throughout the internet?
Here's one source I came across fairly recently
http://www.upsdell.com/BrowserNews/stat_trends.htm#res - the bottom line is that it seems the average user is now viewing at 1024 x 768 or higher. This average resolution always used to be quoted as being 800 x 600, which designers should still try to accommodate, but realistically, the larger resolution makes for more comfortable viewing.
Of course, if all designers stuck to using percentage widths, and ems instead of pixels then maybe resolution wouldn't be so much of an issue! Ah well, that ain't going to happen now is it?
