is longitude and latitude data for UK post codes. US developers can do all kinds of cool stuff with the geocodes they can get from peoples zip codes. Without this long/lat data available for the UK, the mashups that people have been able to do over in the states aren't possible over here.
I was speaking to Ben Metcalfe at the London Geek Dinner about the BBC's project regarding releasing this data and he said they'd met problems with companies such as the Royal Mail who sell this data. Ben said hopefully something should be sorted out. The sooner the better!!!!