I take issue to people who use fixed size, well, anything. Fixed sized fonts are my biggest complaint (especially when they are set at 2 pixels or so…).
Now I realize that XHTML and CSS are not the best tools to work with. Indeed, just trying to get any two elements to line up <i>and</i> have the same height can be a daunting task, but widths…
Widths people, are easy. Instead of going <tt>width: 800px;</tt> and then centering the page, you go <tt>margin-left: 25%; margin-right: 25%;</tt> and be done with it.
Yes I know that then you have to size everything else relative, but honestly, is making your make both usable AND future-proof(ish) really that bad? (yes it is that /hard/, but the end result is something that you can be proud of)
Either most WP themes use absolute widths, or they just set the margins to something stupid like 40% on each side. I have yet to figure out which bit of stupidity it is exactly.
Oh, kudos to the web designers from taking a page out of the programmer’s handbook and instead of making configuration options, just saying “edit the source”.