I'd seen the rotating header image code before and it got me thinking what else you could do with a nice bit of php and livejournal.
So, I've made a PHP page that returns a different CSS depending on the weather in your current area!
It uses a Yahoo weather feed to figure out the current weather and picks from a list of stylesheets you can provide it with.
Well, I thought I'd share it with everyone!
instructions and code at my journal
I'm happy to answer any questions.