Windows 7 - Windows Vista = Windows Vista - Windows XP = Windows XP - Windows 95
So it is a pretty big difference.
I have Windows 7 on both my PC and my notebook and on my brother's laptop!
It runs very smooth but it is not that good for games.
Some people ate shit about Wc3 not working on Vista but it worked perfectly on my Vista and works perfectly on my 7!
One good thing about Windows 7 is the requirement for permissions to edit important things and Windows Defender SO no more viruses!
I have Windows 7 since it was in Beta and I've never had a problem! Anything works as it should!