As an avid registry hacker/editer, i advise against that. As far as registry keys go, they take up little if any real memory.
You can do this instead:
Clear your Pre-Fetch
do not disable it, just clear the list, your next launch of apps after restart will take a fraction longer, but any program which is not on your system anymore will not be able to be loaded into your memory ahead of time, wasting your memory, some of which is RAM.