San Shou (or San Da as it is also know) is a ruleset for training and competition. It involves striking and takedowns (taken from Shuai jiao, Judo, and different forms of wrestling, both Western and Asian).
It is basically a rule-set to train and compete, and many Kung Fu schools (in particular Hun Gar and Choy Li Fut and N/S Praying Mantis) produce San Shou fighters. If you see a Kung Fu school participating in San Shou, you will know it's a real fighting school, and not one of those fruity-cake dancing-in-payama schools.
Some schools allow elbows in their training, but most competitions do not allow it - this is very similar to Kickboxing where you have amateur rules, "oriental" rules, modified Muay Thai rules and full Muay Thai rules (just to mention a few variations). What this means is that, depending on the school, you may train and spar with less restrictions that those found in actual competitions.
Some clips for your enjoyment:
My favorite San Shou clip -
http://youtube.com/watch?v=TcnT3Mx-ZTU
Another great San Shou clip
http://youtube.com/watch?v=RIoNA9iKGc8
Cung Le in Action -
http://youtube.com/watch?v=3r55mxK2xKc
ps... regarding the throws/takedowns, they mostly come (if I believe correctly) from Shuai jiao - at the end of the day, the human body has four limbs, a hip, a torso, a neck and a head, so all effective arts of throwing people on their heads (Shuai jiao, Judo and all flavors of wrestling) end up looking the same.
This is a clip of Shuai jiao if you guys are curious:
http://youtube.com/watch?v=STAzx3dTkaY