I have to agree wholeheartedly with Arch. I don't like fixed width ones at all for the same reasons. I honestly don't see the appeal of fixed width but perhaps it's more something you need to see from a designer's perspective. All I know is that it bugs me too.
That said, I seem to remember reading something in the past about a fixed width having some kind of benefit when it came to accessibility over a fluid one. Maybe someone can clarify if that's right or not?