The question is whether you think your bike is going to be cannibalized by the parts thieves or not.

I live in Manhattan, and I use a thick kryptonite cable and a planet bike u-lock during the day. The u-lock is enough of a PITA to open even with the key, that I'm OK with that. If I'm headed someplace a wee-bit sketchy, I'll bring two u-locks. If I'm headed someplace very sketchy, I take the subway.

The really nice thing about locks is that they are a visual deterrent. If I had a set of pitlocks (funny .... I was looking at them on Peter White's website today), I would still lock everything up.

In NYC, this wouldn't work for long:http://www.missinglink.org/page/how-lock-bike
The main reason is that it looks like someone has already started to take apart the bike. This says to others, "Abandoned bike." You'd come back and be missing your bars and brakes.