Well lets hope Lion is a big advance.
(I barely use Win7 at school, so I'm mainly speaking from what I read, not a great amount of experience like you are.)
I DO use WinXT at work all the time and it's pretty pathetic compared to everything else (course it's 11 years old now). Haven't tried VISTA. CDC is supposed to be migrating to Win 7 soon so I may have more experience. Not sure how all the Fed Budget deficits will impact that, but our IT services are Stone Age now. Horrible, slow, intermittent service.. a real mess. .. and it's NOT cheap.