I think the Vista experience varies. I've been using it to game on for the past 9 months and have been lucky not to experience any issues.

Regarding your store bought system. Was the system advertised as having 4GB? Or was that an upgrade you did? I'm working with one of the larger computer OEMs and they are specifically shipping their systems with 64bit Vista if they advertise the system as having 4GB. Apparently has something to do with false advertising. At minimum, there should be a disclaimer stating that you would not get full use of your 4GB.