I did a clean install from the RC1 to the stable version of Mint 6 64-bit. I did not carry over any Firefox settings except for my bookmarks. Maybe that is why I am having absolutely no problems with Firefox and Flash. I just know I am having excellent luck, thus far anyway.
Even though I do not have an actual need for 64-bit, my hardware seemed to desire it. Granted, I have the basic entry-level specs for running a 64-bit operating system, and I would probably be fine with running 32-bit. However, after my problems with 32-bit ( viewtopic.php?f=60&t=21088
), and the 64-bit version running like a champ, perhaps I actually did need 64-bit in combination with my finicky hardware.
I agree with Fred and Garda in regards to weighing your needs with 64-bit. My hardware made the decision for me, so if it is happy, then I am happy. We all know how bad your day will be when your hardware is not happy.