i probably shoot more lifestyle/portrait work than i do action/sports but with the clients i have there is a fine line from one to the other.  so here are some surf shooting tips:

~ i like wearing a wetsuit for the float factor, 4 hours in the water can get tiring and trying to hold up out of the water a camera housing with a a1ds m2 is like holding a brick over your head while you tread water...oh, and try to take pictures

~ always wear a helmet, you can get one here: http://www.gathsports.com/

~ get a great housing, here are few to check out:
http://www.delmarprojects.com/
http://www.aquatech.com.au/
http://www.splwaterhousings.com/

~ manual exposure, center focus, al servo works best for me

~ at least 12 gig cards, for me that is about 800 images, less time trading cards

~ understand the wave as much as possible and sense where you should be

~ shoot a lot!

~ never eat a large breakfast before swimming out to shoot, trust me.