Macbook Random Shutdown

I had random shutdowns on a week 19 MacBook, sent it out for repairs and then it was gone for a month. While extremely frustrated, I kept my cool and logged a total of 4 calls to the Repair Depot and got them to upgrade the status of my repair and after they did that, I had it back within 3 days. I went to my Apple Store, picked it up and about two weeks later, it started shutting down again. I was pissed to say the least. I went back to the Apple Store promptly, told them my tale of woe and explained to them there was no way I could be without this laptop again for a month and it was just ridiculous to have this happen again. I kept my cool and everything and the Genius completely understood what I was saying and where I was coming from and they swapped me out for a brand new week 30 MacBook, it is yet to shut down on me. From what I understand this is a luck of the draw kind if problem.