If the device does all of the wallet stuff itself, you can take it on the road.
I want this thing to be my wallet. Not a glorified dongle that allows me access to the wallet stored on my PC.
If I remember correctly, ArtForz is already working on a secure key storage and signing device. I'll see if I can find a chat log.
Found it:
http://bitcoinstats.com/irc/bitcoin-dev/logs/2011/05/05/20#l485685Sounds like he and I came to the same conclusions, he just beat me by a month or two.
I really need to start hanging out on IRC.