Don't get on one of Boris's bikes....

... unless you're sure you can find an empty docking space at your destination.

Yesterday's trial experience involved an enjoyable 5 minute ride from Bank to Holborn Circus, followed by a 20 minute search of four docking stations until I found one with an empty space.

Apparently this is because all of Boris's bikes migrate to the centre of London early in the morning - as illustrated well by http://oobrien.com/vis/bikes/

Rather defeats the object - and makes 30 minutes' charge-free use rather notional.