I've never tried to cook low-and-slow on a Weber Kettle Grill, but I've seen it done. Here's a link for those that would like to attempt it for the challenge of it, or for those that want to cook some mouth watering bbq ribs, but don't want to spend money on a new smoker.
I've even heard tell of a legendary competition bbq team driving from Tennessee with two unassembled Weber kettles in the trunk of a passenger car and winning a prominent and long standing KCBS bbq contest in Lakeland, FL several years ago. If that's not validation that good barbecue is produced by good cooks and not entirely by good cookers, then I don't know what is.
We had the good fortune to cook next to this gentleman and his son in Winchester, TN a couple of years ago. What an honor. One of the original pioneers of the bbq circuit--Cliff Weddington and his son Donnie, from Tullahoma, TN.