At first, I was going to remark that the question shouldn't be "security vs. weight" and should be "security vs. security" instead.

Then again, if a thief sees a sturdy-looking U-lock or chain, are they going to decide whether to try breaking it because of its brand and model? That is, is a NY Fuhgeddaboutit going to deter thieves better than a U-lock from *-Mart?

At any rate, I don't find myself complaining about lock weight, not unless I'm carrying it on my back over a dozen miles (I've got to find a better way to carry my OnGuard chain if I want to use it again on a long ride).