I don't normally hop on a soapbox, but this is a pet peeve of mine... sort of the flip side of the coin.
I like nice code. It's easy to edit, etc... I also like to hop around various sites done completely with CSS. All very nice... for a personal site or weblog... I like Mozilla for the tabbed browsing and cool plugins, BUT these guys and their W3C "validated code" buttons make me want to puke.
IF 90% OF SURFERS ARE USING IE, THEN CHECK YOUR FUCKING WORK IN IE DAMNIT!
I can't tell you how many times I have gone to site that looks perfect in Mozilla, and an absolute mess in IE. I don't give a rats ass if Mozilla is better at rendering than IE. I don't care if tables are actually meant for "tabular data" and not images... If your site looks like shit in IE, then you HAVE to change your code. Awww, I'm sorry you can't validate with the W3C, but you have to allow 90% of the people looking at your site to actually SEE it.
There. I feel better now.