Well, many of us have had a bicycle wheel fold on us but there was an article in this weeks Forbes magazine about a Brit. that invented a working folding bicycle wheel. Looks to be about the size of a skateboard when folded up. Guys name is Duncan Fitzsimons.
Appear to be a front wheel only though. A quote from the inventor "I'm getting an incredibly enthusiastic response from everyone but the bike industry." Is anyone surprised? Says he is working on a full bicycle that will fold up to the size of a golf club bag!