Funny we were talking about this on the obligatory cafe stop on Saturaday road ride. I went for the Road ID 2 weeks ago, took 6 days from the states, as i'd hate for my wife/kids not to know (for example) if i was knocked unconscious and in hospital. Reason i went for it as opposed to phone/credit card etc……
1) What if your phone is smashed, lost in accident, pretty likely if you've damaged yourself, camel back tacken off/misplaced etc.
2) A credit card provides no details to the police about emergency contact numbers ie pay as you go mobile for your wife, dads/mums number etc.
3) Tell them where you are/when you are due back – yes you should probably do this anyway, but would you prefer the wife etc to be ringing round all the hospitals unesesarily?
I didn't hink about it much when single and kid free, but having been involved in a serious road accident i think that it's not much to spend for a little piece of mind for your family, even if the new they get isn't good, at least they stand a better chance of getting it.