I keep hearing about thunderbolt.  What does one need to use a thunderbolt interface.  Do most modern motherboards have it built in or does one need to buy a thunderbolt card?

Some motherboards have it, but the implementation has been spotty, and inconsistent. But it has not really been a barnburner for Windows. My personal guess is that it is not ever going to be as ubiquitous or useful as firewire never was and USB is. It is coming along when most of what it has to offer in windows is irrelevant, as the computer becomes just an appliance for checking social media. This is as close to a fanboy review as you are likely to find.
 
http://www.anandtech.com/show/8529/idf-2014-where-is-thunderbolt-headed
 

Interesting.  thanks