"Growth Marketing" at its finest. The quick summary is that if you give the machine access to your Twitter account so that it can tweet out an advertisement "from you" it will dispense you a pre-made burger. No doubt its one per twitter handle so be sure and have a bunch of pre-made handles ready for it.

As with most things, such systems are equal parts clever and stupid. The gamers in the crowd will get free burgers with day old twitter accounts that have specious handles like @NeverBelieveMyTweets or @ShillingForTheMan etc. This will cause McDonald's to hastily try to push updates to the software to check the ages of accounts, handles with bad words in them, etc. And of course it is "working around" a number of FTC regulations on implicit advertising in exchange for free merchandise (those tweets better include a disclaimer!) and the cash starved company (Twitter) itself is not seeing "advertising" or "promoting" revenue (it would be really interesting if the BigMac machine tries to use your account to promote its own tweet from your account).

So once again we have a "brilliant" idea where if it is only used in exactly the way they want it to be used, would be brilliant, but is so easily exploitable that such use will likely be overwhelmed by mischief resulting in a much more costly campaign.