Until last year I've never used a torque wrench on bicycles, only on cars. But when I started assembling parts for my first modern road bike, there was no way I would go without a torque wrench. Tightening the expansion plug in my Reynolds CF steerer or the tiny, tiny titanium bolts in my Deda stem without a torque wrench would not only scare the hell out of me while tightening, but would scare me every time I rode the bike. Even using a torque wrench I still managed to snap the head off a pinch bolt on my Ultegra SL crank. These bolts are so small and with such fine tech specs, I think they should even specify the number of re-torqueings they can handle. As for the usefulness of a torque wrench:

If it saves your life just once, it's probably worth it.

<edit> When I started assembling my bike I borrowed a friend's very nice and very expensive micro-adjust Pedro's Torque Wrench while I waited for my pedestrian Park beam wrenches to arrive. I actually find the beam wrenches much more efficient. There are so many bolts with so many different torque specs that it's a pleasure to just grab the beam wrench and go instead of turning the micro-adjust handle a whole bunch of times between each bolt.