Although we caution people that cable locks are not as secure as U-locks, it appears that big, thick cables are a reasonable deterrent if personal experience is any guide.
I'm in campus law enforcement, and we deal with bike theft all the time. The common cables that run anywhere from 1/4" to 3/8" in diameter are essentially useless; even a small bolt cutter will snip them instantly.
However, I can't recall a case where someone took a bike locked with one of those big 3/4" or 1" braided cables... Theyr'e too big for most bolt cutter jaws and take too long to saw through.
A good Kryptonite is better, though.