Well defenately lame, sorry it happened, i've had someone go afk in a match but never on purpose. Like they said get a SS and post it in the Hall of Shame next time so the community can shun them.
What you'll soon find more annoying than that is beating good premade with your PuG only to have them all quit as they're about to lose and the game does not get recorded at all its a real heartbreaker.
Oh, I've had that happen. Very frustrating. I wish there was some sort of built in game mechanic to vote against griefers to have them removed but we all know that has potential for abuse as well. I believe I got a screenshot of my teammate saying he was going afk and that he'd be back mid-match(never showed up!). I'll see if I can find it.
Edit: I have no proof that this happened. I was foolish enough to copy something after taking my screenshot. I suppose my point is invalid but I'd at least watch out for these guys.