http://labs.adobe.com/technologies/flashplayer10/
http://labs.adobe.com/technologies/f...yer10/faq.html

in short:
linux gets it first this time: It gets the first 64 bit version of the flash player so that they dont need wrapper tools to get the plugin running in 64-bit compiled browsers on a real 64 - bit Operation System.
Many Linux users complained about this massivly for many years. The plugin however is not yet completed,- video, microphone and fullscreen features are not yet completed in 64 bit.

There wont be noteable performance boosts for now as the flash player already seems highly optimized as it is today in 32-bit.

Later on OSX will follow and lastly sometime windows XP/Vista/Azure though windows already has downgrade emulation in their 64-bit Operation systems so it wont hurt there.