I was really pleased to see that Network Rail have released their live feeds. There seems to be lots of potential.
After a steep learning curve in Activemq and STOMP I finally managed to get a ruby program which tracks trains. I was pleased with this but then realised that one of the key components appears to be missing. ALthough there are various time codes there doesn't seem to be any way of identifying where a train actually is. I'd have though most useful applications would need this. There must be a clever way to get from the GB Train Timetable to a train's location but that doesn't mean much to most people. What's need is a lat/long grid reference and then this feed would be really useful.