Happened to me right after I started soloing and the worst part about it was that I didn't know why. Right after touchdown it felt as if the plane was being lifted up and pushed off to the side... I never hit grass but it certainly wasn't pretty.
Cause:
I figured out later that I must have just released the rudder on touchdown. Seems to be a common mistake if you look it up for beginners
Further if you need to know that everyone has bad landings watch these monkeys
http://www.youtube.com/watch?v=V9EYYaJxRGY