While the retail clinic market has grown dramatically, experts still bicker over whether these clinics represent a long-term shift in the marketplace or a fad which will fade out over time. On the one hand, retailers seem to be buying into the concept in growing numbers, note authors Eben Fetters and Ron Luke. But on the other, some smaller operators have already closed or lost their retail locations. Other observers wonder whether primary care physicians will simply take over the potentially lost business by offering competing hours and levels of convenience. Column