I've been to the page now about 20 or 30 times, but only just noticed both a "Sunset" and a a "Night Campfire" version of header background! Perhaps there are more?
Do they cycle through in a 24 hour period? Are they timed to the server time (central european timezone I guess)?
Cute idea, to have the sky and horizon silhouette keep time with the sun - as it appears to be doing!
Hah! Finally somebody noticed it :) There are two themes, one "day" and one "night" theme. And they sync to your local time :) If you're using Firefox, you can also choose the style manually from the "view->Page Style" pulldown menu :) We thought about making something more sophisticated, but we didn't want to use flash and everything else is a browser compatibility nightmare, so we kept it simple :)
I noticed is as well some time ago and I also think that it's a very good idea. ^^
nice one!