Just backed. Very slick.
Been researching pay-as-you-go data SIM cards as well. Found a T-Mobile reseller Lyca Mobile for $0.06/MB with free SIM card http://www.lycamobile.us/en/national-plans
Others have recommended Truphone: http://uk.truphone.com/personal ($0.15/MB)
I expect data to be only used when bike is stolen, so pretty much a free security precaution (albeit with spotty T-Mobile service). That is, unless I'm missing something.