My preference is 80 - 95%, NOT pixels. Pixels means fixed width and that is poor design in my opinion. The width of my flooring forum works just fine in a monitor with an 800x screen resolution, but it also looks good at 1280x. I hope someone will be able to develop a way to determine the size of the user's viewport and adjust the width of the website to suit. This way, people using, for instance, a 1600x resolution and full-screen display of the browser can still view my site in comfort.
PS: I believe the standard size for those that do use fixed widths is 760px