Every computer, keyboard and laptop should come with one these days. Whether it's built in, on a USB cable or available in some other way. Not just business ones.
They're bloody brilliant.
My new laptop has one and it means if I want I don't really have to type my password any more for a lot of things, especially logging in to and unlocking Windows.
It's a shame it's not currently supported under Linux but I assume support will come eventually.
It does depend on having some decent software to sort out browser and program logins and thankfully the software provided (DigitalPersona) isn't completely shit.