well my commute today got me all of three miles up the road, at which point my rear wheel started wobbling around, then jammed, leading to the chain being thrown and wrapping itself tightly around the rear sprocket. Closer examination revealed two broken links in the chain, four broken spokes and a distinctly un-true wheel.
It looks as though 5 years of all-weather commuting have taken their toll on the ends of the spokes and once one had detached itself, the others were happy to start following. The spokes on the front wheel aren't looking too great and the rim is well worn, so it's two new wheels. The chain was due for replacement anyway, being about a year old and starting to sag. And while I'm at it, I'll gear up by a tooth or two, now that I know what gear I've been riding (see discussion on gears on Velo Fixe).
Happily, this happened in an empty bus lane at a relatively low speed, and it wasn't too far to walk home. I'd hate to think of it happening as I went round, say, the Elephant and Castle roundabout.