Yeah in the old days it performed quite bad. Nowadays with the newer distro's like suse 11, (k)ubuntu and a couple of others I really havent found any more glitches than on any regular windows machine running flash..
I develop with flash regularly on my Linux machine (Ubuntu 10.something), and it's definitely a bear compared to windows. I'll be happy for the day I can walk away from flash, but it makes computationally intensive consumer applications much easier/feasible. When we started out project almost three years ago, it was such a clear winner over JS, but now it's becoming a wash.
I code Flash too, on 2.26 Ghz laptop running 4gb and multiple distro's, no real problems here..
A lot of us Flash coders actually want to drop Flash from our websites, widgets and resumes. It performs bad and puts a lot of stress on the CPU, blocking my vital programs from running.
I've been coding Actionscript for some time now, but only started really liking it when 3.0 came out. I remember when the Papervision project became popular I loved coding Actionscript.... I still do and I dont think JS has the right properties to become anything close to Flash.
64-bit Linux is even worse, as it has to go through a 32-bit adapter to work in 64-bit Firefox. Video is unwatchable for me on a Core i7 with a fast video card.
Yeah, I use a 32 bit compiled version of firefox called swiftfox for all my flash debugging/testing. Definitely slow as heck, but, faster than using the wrapper/adapter method.