The rim on my rear wheel (a Mavic Ksyrium Elite) got a nice dent and bulge this evening from hitting a large chunk of metal that was lying in the road. The chunk of metal punctured my tire first, which instantly deflated the tire, and then the rim landed with a thud further up on the piece of metal. It isn't cracked. I had my LBS look at it and they think it is still okay to ride, but it got me wondering how big would a dent have to be before it would be necessary to replace the rim.

Thoughts? At what point would you decide to replace a rim because of a dent?