Its not hard, but man do I HATE doing it.  I need to get new sanding pads for my festool sander than junior coerced me into getting.  It connects to a vacuum and definitely makes the job a bit better.  My biggest issue with doing them at clients houses is that most of my jobs are small one day deals, and drywall repair will require multiple trips in most cases.  There is quick drying mud, but I haven't worked with it to know how feasible it is to get any patches down in a day.  The other issue is it still would require paint.  One thing I hate more than patchwork is paint, and I am definitely not painting a clients house.  I am an AV guy, not a painter.