I was using a rather stout cable lock for a long time, the combination sort, this is also what I carried on tour. On tour I didn't have to carry ANY keys, didn't want one for my lock either. I used this same combination cable lock around town when commuting but only ever locked it outside of stores, most often while grocery shopping, lots of foot traffic.

One time while stopping in at a grocery store on my way to work the combination lock malfunctioned, wouldn't open. I went into the store, bought a $5 hacksaw and sawed through the cable. Total time lost including finding and purchasing said hacksaw - about 15 minutes. Took me about seven minutes to saw through the cable, first time I ever did that. With minimal practice I could do it in under five. No-one among the many people passing by questioned what I was doing.

Since then, I only go with one of the higher-rated u-bolts, I'm not really concerned that its overkill most places.

OK, as long as no one realises that them two Ortleib panniers just lift right off the rack ( ) I'm good.....