IMHO charger on my late 2011 Macbook pro is a better design and i'm not sure why they moved away from it. Without getting into the discussion of the plug face changing, this one does come undone way too easily.
Within my first half hour I had accidentally unplugged it 5 or 6 times, just by moving it around in my lap. Pick up the cord and plug it back in each time, it starts to get a little annoying.
I've gotten better with it now, but I will still do what this video shows, where it doesn't completely unplug. You don't always notice until you get a low battery warning when you thought it was plugged in the whole time :(