In reply to Pids:
The bike rack where I work seems to have a good assortment of things available to nick on most bikes - lights and even saddle packs. On the other hand, I'm not aware anything's ever been nicked, as it's in the depths of a business park and thieves are either too lazy to go there or would be picked up by site security.
I don't leave anything on my bikes when I park them anywhere, out of habit.
Only thing I've ever had nicked at a station bike rack - apart from the occasion where someone nicked the whole bike - were the quick releases from the wheels! I found a couple of bits, could see a couple more bits on the track and no sign of the rest. A few other bikes had also been done. That was a long walk home late at night
I now have anti-theft skewers on anything I'll leave at a station.