piatkow - 7:09 am on Apr 12, 2012 (gmt 0)
1. The larger the screen size the less likely a user is to have the browser window set to the full screen size
2. Small screen devices are becoming increasingly popular.
With the range of screen sizes and connection speeds both increasing it really isn't possible to create a "one size fits all" web site any longer. Personally I would keep layout as flexible as possible to minimise the need for code to detect specific browsers/screen sizes.