[Tom_mac]

does shape shifter slow down any one elses computer

[cgc]

Only if your computer is old. Heck my Sawtooth (400MHz G4) seems the same when using or not using ShapeShifter.

[Visualize]

It should only slow down your application launch times because it has to inject code in the application each time you launch an app. But for a moderatly new Mac there should be no problems- not noticeable. We're talking less than a second in difference in application launch time.