Also running a 64 bit machine - the details are available in the More Information link under my avatar:
I'm not a big IE fan at all. As a matter of long, long practice have run anything *but* Internet Exploder - and that's going all the way back to the Netscape days. Take the following with a grain of salt, since I've done no repeatable/measurable testing.***
Anyways - I installed IE and when that ran satisfactorily for most of the last week, I went ahead and tempted the fates by adding 64 bit Flash.
Even at a glance IE9 is significantly faster than 8, and is also faster than the the Firefox 3.5.5 (with a small list of add ons) install that I have on my current main box. The UI is small/sparce, and very Chrome~like. Except being MSFT, they have to put their own 'touches' there. Still - A huge improvement over what came before. I won't conjecture on whether it's enough to make me utter the blasphemy which would be an implication of acceptance of a MSFT browser. But it's surprisingly non-painful.
Flash - I just did this morning - so the most I can say at this point is that you can use the flash apps at sites like BMW USA and Mercedes Benz to build yourself a car that you could never afford. So "64 Bit Flash Works", though the question of 'How Well' is still up in the air.
***I did head to the ACID test site.. but for some unfathonable reason known only to the DIA, CIA, FBI, and Elmo The Muppet (not necessarily in that order, either...) the site was inaccessible when I tried. Couldn't possibly be the first public release of a new Browser.... So it has to be a global conspiracy - I'd go into more detail, but it gets kind of vague and confusing around the part where to prove the theory you have to place Jessica Alba's underpants over your head in the presence of the Pope (YES!! There *IS* a God!!... and then yo