I remember trying out Longhorn when it was released, and couldn't get over how - from the start - it used over 1GB doing nothing. When Vista came out, this didn't improve.
The UAC was - and still is - painful to use. I know Linux uses the same sort of confirmation but it was/is far less annoying than it was on Vista. No idea why that was, maybe it's because for every little thing I needed to put on there it needed to be clicked. Whereas Linux it'd ask me once and let me carry on for a little while.
But it won't be missed. The only one worried about today is Windows 8. The clock on the wall is going tick tock for you my friend.