@Greg - Thanks for the comment, Greg. Glad you like my entry...
Know I'm not meant to be promoting on here, but there are a few really well marked-up skins from a technical stance, Mark's being one of them. But Tracy Wittenkeller's, (*ahem*) mine, Cuong Dang's, Armand's and a couple others are lean, mean, full XHTML / CSS skins - some totally tableless.
@Jeff, Greg and Others -
If you are interested in seeing the source simply "View Source" in your browser. And if you're interested in how these sites degrade when you disable the CSS styling (the stack flow), get yourself the web-developer toolbar for FireFox, and disable all styles (Menu > CSS > Disable Styles > All Styles). With the same tool, you can also view the CSS. By doing these three things, you'll get a better idea of how these sites and skins have been put together.
The judges though have no doubt gone through all the nitty-gritty technical details and selected the winners accordingly. Like Timo has confirmed, you're only voting for your favourite - and it is a tough choice...
I couldn't agree more on the level of work - all round - well done and good luck to those that entered and well done to the Experience guys for pulling it off.