It is very colloquial and sounded dated to me (my mom says this, I don't). I would use the words "master" or "memorize" (in the case of vocabulary). It's fine to use it, but I personally avoid it because it sounds kind of rural (like maybe you don't know the words "master" or "memorize"). I mean no offense to anyone when I say that, it is just the sociolinguistics of my area!

Yes, it is very common. As an aside, if you rearrange the words to read, "get pat down," the meaning is totally changed and means that the person is being searched for weapons (presumably by the police).

I agree with Patrick. It is something people in more rural areas say. It is definitely informal and not as common, although you will hear it. It is good to know what it means, but probably not as good for you to use.