Since moving to Chicago, my coworkers have warned me against bicycle thieves. Even if your bike is secured with a gold standard U-lock, thieves can still strip your bike with Piranha like vigor. I've had back wheel stolen when I locked my front wheel and vice versa, I've had my gear chain removed, my lights stolen, in one case my break, I've had my frame dented when a thief tried to, I assume, yank my U-lock out of its cylinder, a co-worker recently had their saddle stolen,. Most of this stuff isn’t so much valuable as it is an inconvenience. The lights on my bike new were 10 bucks. I try to imagine there's a huge mark up for used Cricket bicycle lights or Shimano chains or something, which would warrant such thefts. I've looked at my fair share of high end complete bike locks, most of which involve cables cumbersome to set up, in the case of chains, weigh you down, and in the case of cables can be cut with a pair of mid to heavy weight bolt cutters if the thief knows what they're doing.