Another new feature to Gingerbread is Near Field Communications (NFC). It's a fancy term for wireless communication between things that touch each other. You've probably seen this with your current credit or bank card, and special terminals at places like gas stations or bank teller machines, and it can be pretty handy. It's a smartphone technology that's still in its infancy, has little practical use currently, and needs specialized hardware -- currently only the Nexus S supports it.
We expect all that to change soon, and a new series of possibilities -- and security concerns -- will become the norm in the smartphone arena. For now, unless you're in Portland and visit one of the businesses Google targeted in their Hotpot testing area, there isn't much you can do with it. But for kicks, get out your bank card or passport and hit the break to see a demo.