While MS did use ideas from FF and Chrome, a lot of what they are doing is ahead in some ways. I tested IE9 vs FF4 and IE9 was more compatable with a slew of things FF4 wasn't and overall at the time IE( was faster.
But there is supposed to be a new RC of IE9 out tomorrow or so its rumored.
They made a lot of changes, bug fixes and enhancements to it so hopefully its even better.
I like FF for some things but IE9 has great HTML5 support and so far loads faster to start and loads web pages faster than FF.