Honestly, I wish their use would expand into other areas of our lives -- replacing username and password combinations for various devices (working for an ISP, home routers are one good example).
As much as I'm against the idea of a mandatory "national ID", I'm convinced that it will happen someday (in .us, where I live). When it does, I believe it'll be something similar to US DoD's CAC [1]: a physical identification card that doubles as a smart card. The private keys stored on the card will allow you to prove your identity to your banks/financial institutions, e-mail account (100% encryption of all e-mails? Yes, please!), and so on.