Didn't want it to fubar my existing perfectly working XP install, so I installed it under Virtual PC
After the hours of installation and watching it eat up over 8gb of disk space, my first impression was "Hmmm, fluffy user interface, pretty, but where's the "classic look" checkbox?". Followed by security dialogs ("Windows needs your authorisation to blah blah...") with no useful information in them - telling me a program is trying to do a "user control operation" or "file operation" is completely useless if it doesn't tell me exactly WHAT that operation is for. It doesn't even say what kind of file operation - I'd certainly be more cautious of a delete operation than a simple read for example.
So at the moment, a few nice touches, but it seems completely over the top and bloated in the "Lets make it look pretty" and "Can we make Windows any more annoying than it already is?" departments.