I keep a 32 bit OS (XP) running on a virtual machine, in case I need to to run some very old software that won't install/run on the latest Windows. But in general I would only use a 64-bit OS on my main computer, because fewer developers are supporting 32-bit versions of new software.
I remember a stack of old 16-bit 8086's at work that had been in a closet for many years... I should have grabbed one of those chips... just to keep a little piece of computer history.
I've been running 64bit OS since release of Windows Vista. Yeah, that one. It was the first OS that had reasonable 64bit driver support. WinXP 64bit Edition was something I preferred not to bother with since support was pretty bad in general.
I dont even remember how long it is since I used 32bit. It was in the XP days. I wouldn't mind using 32bit, if it was just as safe as 64bit, and could use at least 8GB RAM.
I liked XP though.