| The key variable in your question is "too much" - what is too much? At the extreme, yes, if you buff with a really abrasive compound for a long, long time - yeah. But in general, orbital polishers are very, very safe.
Even rotary buffers usually do NOT cause damage as a direct result of polishing when the pad is flat on a flat surface- they "burn" through the paint by producing too much heat, typically at an edge of the spinning pad, where the pad speed is highest - and usually because that edge wasn't in the focus of the operator and contacted a different surface on its side or edge.
Orbitals don't spin at any great speed, so they produce very little heat. You have to really, really work hard or have a complete lack of reasonable common sense to damage your paint with them.
Just about everyone on this board who already uses a Porter-Cable machine will tell you it saves time, produces better results and is easy to use. There is some technique to using it properly - but failing to get that technique right only means a less-than-perfect shine - no permanent damage. | 
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