When traveling, I love to buy kits! On a recent trip to the Oregon coast, I bought 3 kits, each put together by the local shop owner. Since each of these kits came from small LQS's in Oregon, I'll never see them here in Northern California AND when checking the price of fabric, sometimes buying a kit is the cheapest way to go. In my opinion, using a kit is no different that using a mass-produced pattern or following a pattern in a quilt magazine.
I've never purchased a mass-produced kit, but I do love those put together by quilt shops.