It was mentioned a long time ago when Ultimate features were starting to
emerge. MSFT at one point was, probably still is, marketing Ultimate for
gamers citing the feature. Paul Thurotte mentions it on his site, although
without going into much detail about it. Also the Wikipedia info on Vista
Ultimate mentions it too.
In fact, it's mentioned so much and so often that I thought it had to be
part of the core Ultimate edition, but could not find it at all.