Funny, because I had an laptop that came with Vista SP1. Later when I upgraded it to Windows 7, I wondered why I even bothered since it looked and performed exactly the same.
And I had a laptop that came with Vista. It was totally unusable. Then SP1 came out and it became mildly usable. Then I got Windows 7 on it and the difference was like night and day. Boot times were cut by far more than half. Time to usability after login, likewise. Responsiveness increased dramatically. Crashes reduced likewise. Windows 7 in particular uses less memory than Vista; Vista chokes on 2GB systems and doesn't become acceptable until 3 or 4GB, and 7 is acceptable in 512MB and fine in 1GB. This is not a big deal today when RAM is practically free — I have 16GB in my budget desktop, and that only because I like to run virtual machine and keep them running while I run big, memory-hungry apps. At the time, it was a big deal.