http://www.treehugger.com/files/2009/11/velib-bike-sharing-thieves-vandals.php

80% of the bikes are missing or damaged.
They cost $3500 apiece, resulting in a brisk black market.

3000 were stolen the first year.

The idea of a distinctive appearance did not seem to reduce theft.
The bike are either stripped for parts locally, or exported intact.

http://redjar.org/jared/projects/communitybike/summary/
Nice summary of community bicycle projects.

D: I am unfamiliar with it, but I have heard of a European antitheft mechanism.
I think it locks the front tired in position.

http://www.baltimorespokes.org/article.php?story=20080910095417936
D: a campus that has GPS-equipped 'bait bikes'.

D: I thought an RFID tag could also do so.
Even just equipping major intersections in big cities would eventually flag down many stolen bikes.
I've seen RFIDs claiming a useful 40' range.

http://www2.giant-bicycles.com/en-us/bikes/model/city.storm/3884/36268/
D: an almost perfect city bicycle.
And only $1500!
The frame is aluminum.
I guess that makes the weight tolerable.

As I get older, I like a nice sensible modernized Dutch cruiser more and more.

http://cityroom.blogs.nytimes.com/2009/04/30/dutch-to-new-york-ride-our-bikes-please/
D: here is a modest $800 Batavus Dutch cruiser.