Molly Holzschlag asks where the diplomatic middle is in her post Fixed Versus Liquid. I have a preferences which we will go into, but it really is a nice happy medium.
The general idea is that navigation isn't where you want to expand the page, but the content is. This approach also draws a line in the sand and says that the center content can only expand or contract within reason. This helps keep a page readable by keeping text from running into oblivion on those 30 inch apple displays, and on the 15 inch displays.
I like a leftnav of 170 pixels wide, and a center content that is liquid between 530 and 830 pixels wide.
There is even a really cool example page.