My next door neighbour is a family doc.  We've had some great discussions about this issue and she has advised me time and again that the doctors are far more creative in avoiding taxes than the government is collecting it.  This doc also said the Ontario Family Care Clinics have been a financial boon to the doctors and a drain to the taxpayers.  Once again the view was the doctors continue to outmaneuver governments in the government's attempts to get incremental value for every dollar spent.