Most users will notice little if any functional difference, apart, perhaps, from the execution speed of some operations and enhanced multi-threading/multi-tasking performance. Most 32 bit software which works under Win XP/Win 2K should function pretty much as designed when run on a 64 bit system; everything I've tried so far does (with the exception of some things like certain browser extensions). Little actual 64 bit software is out there yet, but that will change rapidly as 64 bit hardware becomes more common.
From the consumer standpoint, the greatest impact will be in the area of Audio/Video performance, with absolutely stunning developments to be expected in gaming as product is developed to take advantage both of the new architecture and of new developments coming in higher-end graphics cards.
A good article may be found
HERE