There are times when a small bump on the road made the suction cup lose its' grip. Other times when it's mounted with the phone attached, it would slide either clockwise or counter-clockwise, depending where most of the weight is if you don't balance it evenly.
So for now its collecting dust. Maybe try it on another device (like an iPhone) with a Kraken case or mod a better suction cup to it.
Galaxy S2 ShoStock 1.9.4