Facebook's "Like" is surprisingly new; I found a Mashable article[0] from the day it was released in April 2010. Digg, on the other hand, is surprisingly old[1].

[0] http://mashable.com/2010/04/21/facebook-f8-2/

[1] http://en.wikipedia.org/wiki/Digg

Probably not, but K5 probably does.