I've been using Linux since 2006 and started with x86_64 Ubuntu before moving to Arch x86_64. I've never used a 32 bit version of Linux. Flash was a bit fiddly early on but not for a long time now and has certainly never made Firefox unstable for me.
I'd consider myself an "average" user and 64 bit was the obvious choice even back in 2006, as things like ripping MP3s is a lot faster. Seems like a no-brainer to me. And I never ran out of memory with 1 GB either (using 8 these days).