MAC locks won't do anything for PC. People will just spoof their MAC ids.
But I do notice a LOT less cheaters since VAC was implemented. And my rank overnight went up 3000, so I'm guessing they reset or banned quite a few people. If think someone is cheating, I just leave that game wait a few seconds then rejoin. Most lobbies don't have cheaters anymore; whereas, it used to be the other way around.