Hi,
Chances are you wont know me but i am Chewitt from the XDA Developers, i have created 6 themes for the X10 and they are currently posted up on the XDA Developers site, i think that a Themes Sub Forum here would be a great addition as once we have the boot loader cracked and user friendly there will be an increase in people creating themes for the X10.
Regards,
Chewitt
PS if you want to have a look at the themes here is the link.
http://forum.xda-developers.com/showthread.php?t=737778