The article linked below revisits a worrisome issue. Do state and federal laws against kick backs for referals apply to services like Groupon? Personally I find it a stretch, that has nothing to do with the original intent of the laws. Never the less the issue has been brought up, so be prepared.
With the rise in popularity of daily deal sites like LivingSocial & Groupon, there has also been increased scrutiny as to the legality of this practice and whether it violates any ethics rules for doctors.