I've gotta admit that I was confused the first time someone told me that he "hearted" me for something. It felt a bit dirty to be honest.
Turns out that "hearting" is how one adds friends using the Gizmodo commenting system. You just click on the little heart next to another person's name and boom-ba-boom, you're done. Now you'll see that person listed on the "Friends" section of your profile and he or she will see you listed as a "Follower" on his or her page—no Facebook-style confirmation procedure necessary.
There's no definite guideline as to why you should "heart" someone, but it mainly seems to serve as a way to tell someone that you think his or her comments are awesome. It also makes your favorite commenters easier to spot in the comment sections of posts because they'll have that eye-catching bright red heart next to each of their comments.