One was the permissions to run certain applications went away.
A good enough reason in itself!
Also I have to reboot less often due to when the system hangs up.
And since it is 64bit it uses all of my 8gb of ram.
My Vista at work is painfully slow, so slow in fact (with 4gb ram) that I took advantage of a Norton £10 offer to speed up my PC.
Some friendly chap from the Philippines took over my PC for about an hour - apologised for the long delay - and left it exactly as it had been an hour previously.
When Windows is new, it runs like lightning. Six months later, it doesn't want to know.
That never used to happen when I ran Linux systems
Although (I must admit) it was a nightmare to install anything 10 years ago. Ubuntu these days is way better.