This width is designed to fit on the width of what I deem to be the smallest screen that a reasonable number of people are using (on PC’s – not going into mobile phone handsets and the such). That size, in my belief, is 800×600 i- the initial Asus PC’s, which sold so well this year, were exactly that.
However, the width I’ve been using has been very much a “finger in the air” affair – so much so, that the appearance of a vertical toolbar causes the horizontal one to appear in some cases. Yep, I got it wrong.
Firefox uses 17 pixels and Opera, well, god only knows – I got strange results. Without a vertical scrollbar, it took up (strangely) 1 pixel horizontally. However, introduce the scrollbar and it took up – the same. It would allow my image to be 799 pixels wide and not bat an eyelid. Make it 800 though and the scrollbar appeared. Why this happened I honestly don’t understand. But I’ve tried a 779 wide page and that works, so Opera is certainly not using up more than the “magic” 21 pixels.
Konqueror uses 19 pixels and Safari (on Windows) is the slimmest at just 15 pixels.
The Copy+ site has already been converted to this new width, and the BMTG site will be soon too.