My security key arrived last night from PayPal/eBay. I've activated it, and it seems to work pretty well. They're in the early stages of deploying this, but for $5, my accounts are a lot more secure.
Their implementation requires you to login with your username and password, the way you do today, but then also requires you to push the button on the front of your keyfob and enter the six-digit code that appears there. The code changes every 30 seconds, so that even if someone does see your code, they have very little time to do something with it.
If you use PayPal or eBay much, I'd suggest ordering yourself a key as an extra layer of security on your accounts.