A longtime friend who lives in Amsterdam says that the going estimate is that 40% of the bikes in Amsterdam have been stolen at one time or another.
He and his partner have six-eight bikes between them (that number includes a couple of sit-up-and-beg bikes for visitors, which live outside chained to the downpipe.) As fervent Bromptonistas, they keep their special bikes closely tucked underneath their arms, so to speak.
Those bike-retrieval machines and routines are something else, though -- I can understand why the crowds gather. Reminds me of a friend who moved to Ottawa from Vancouver, and in the middle of the night, after the first real snowfall, he spent an hour-plus watching the giant snow-removal machines, a complete novelty for him -- all blue lights flashing and beeping, and a symphony of whirring, clanking and scraping. He said he thought he was in a set from HG Wells' "War of the Worlds".