A cyclist I know was riding the bus through Minneapolis a while back, with his bike on the drop-down rack. Another bike was in the front slot; his was nearest the bus.
When the bus came to a stop downtown, a man ran up and quickly snatched the other man's bike and rode off.
It's a pretty easy procedure — just lift the retaining arm so it clears the wheel, drop it down, lift the bike, run until clear of the bus and then pedal like hell.
The bike owner ran off the bus and started to take the other guy's bike so he could give chase.