Yep, things are looking pretty hot out there From time to time I see a comment on a skin from someone saying they "can't" use it because it's a Win7 theme. A lot of times the Win7 themes work pretty well on XP (and look great) as long as a person doesn't obsess about the few oddities. So, shy XP users, go ahead and give them a whirl, there's always delete
I find the WindowBlinds 7 skins work perfectly well on my Vista system. So if all future WindowBlinds skins are made for Windows 7 only, it would not be a problem for me. Don't know about the XP'ers. 