...How much better do you think it is than Vista?
Problem is Win7 is based on Vista anyway so any improvements you have Vista to thank for the groundwork.
Personally I had no issues with Vista especially after SP1,not to meantion drivers are now thick and fast for both Vista and 7 nowadays(remember you can even use Vista drivers on 7 at a pinch),so I would have to say its an improvement with older/slower hardware,however stability wise its the same for me since I had no issues in that area,boot times etc same for me since I have both Vista and 7 running sweet.
Some problems with Vista I would even put down to user error as well,believe me you would be amazed at some of the excuses I have heard where it turns out to be faulty hardware and not the OS,problem is everybody likes to blame Vista when most people don't have a clue what they are talking about.
Bottomline Win7 is an improvement on Vista with older hardware but Vista is still a good OS in its own right,anybody that says otherwise should not be building or using PCs and should stick to consoles.
Win7 is probably best OS so far by Microsoft IMHO ,I have high hopes for Win8 to be even better ,only time will tell if I'm right.