It doesn't mess anything up Alistair, I've been running windowblinds for a few years now. There's no GUI issues. That occurs mostly when you fool around with your log-on and/or Windows start-up screen. Right now I'm using a MILK theme. I switch every now and then when I think I'm getting board. I have a Mac and PC,
running through a switcher to 1 24"monitor and mouse. I like the custom themes because 1) Gates' designs suck and 2) all the controls are 'Mac' format [left side] and my mind isn't so quick anymore. Here's a look at it.
http://img420.imageshack.us/img420/1329/screen0nn.jpg
If you want to see a 'trick' desktop, check this out I simply runs over your desktop, it doesn't replace your theme.
http://www.lighttek.com/talisman.htm