I just switched to SPD-SL pedals/cleats, and am still getting used to them, but that will come in time. The only thing I don't like about them is my old SPD pedals were a full platform and could easily be ridden with sneakers when just going for a casual spin. I'm doing a 250+ mile ride over 5 days this summer, and will be venturing out looking for sustenance (and beer) after pitching the tent. I'm half tempted to put a pair of platform pedals into my duffel bag to switch out for the evening local out-and-back for dinner so I don't have to deal with my road shoes, but I'll stick with the clipless for the serious daytime riding!!
+1 on Biker395's admiration for toughing it out with the tennis shoes!!