I tried the hill start assist feature for the first time - on an incline that read 10 degrees in the truck apps, so it was pretty steep.
I have to say I am VERY impressed! That thing works extremely smooth, can't even feel it - it just does it's job when you press the accelerator.
So it holds the brakes for a few seconds. If you don't hit the gas during that time, it will let go, and you roll backwards as without the feature, until you step on the brakes again. Then it repeats. When you step on the gas while it is holding the brakes, the brakes are automatically released, very smoothly. Honestly, it feels like on a level surface.
Awesome, this will be handy for tight trailer maneuvering and hill starts!

 

Yeah I wish my 2011 had this (one regret for not waiting but there are no LL's in 2012). I have this on my other car and while it's not "necessary" and I can get by without it, it is a nice convenience feature after you get used to its operation (the first time will feel weird).