This functionality currently exists for any
online password on Windows/Mac/iOS in 1PassWord, and I'm sure there are many other wallets and password managers for other platforms that do similar things. Having a USB key for this almost feels like a step backward - how do you plug that into your phone or tablet? 1Password will automagically enter and submit any remembered password in your browser, and any non-web password can be stored and retrieved from the app itself at any time. I didn't even care about that feature when I bought the app, but it has become a lifestyle changer for me and I'd say it's the killer feature.
The worst part is, I can buy 1Password for Mac for $50, and the iOS version is less than $20. Anybody interested in this sort of thing should really check out the alternatives already!