It took me a while to work out what was going on here. Thankfully I followed the link before I started babbling on about how impressed I was by his superior grasp of technology.
The Telegraph has a feature on Twitter today (well, Monday), which goes a little way towards explaining the why, if not the how. Useful in earthquakes, apparently. It strikes me it would be useful at Party Conference when people are trying to arrange meet-ups, or to let people know what reception they've popped into. Although at conference there is always someone you're desperately trying to avoid who keeps turning up in the same place as you, and they'd be bound to be the sort that would be following absolutely everyone's tweets. (Is that the correct term? Using it feels a bit stupid).