Some good point from several people re: avoiding attack.
Couple of things though.
First: Great Whites (can be over 7m and 2000kg) do not eat nearly anything. There food sources change as they grow. Smaller Whites eat stingrays, fish etc, as they grow their focus changes to larger prey such as turtles and more often dolphins, seals and other sharks.
If you read accounts from great white attack survivors almost every single one did not see it before they were in its mouth. If you keep your eyes open (not always possible especially when the water is dirty which is not what whites like anyway) and spot them they almost never attack. Some how they know they have been seen and are very cautious.
Great Whites are ambush predators that love deep gutter along beaches and around out crops. Here they can cruise close to the bottom and see the silhouette of prey above with there own counter shading making very hard to see them below.
Once ready they go for the prey as hard and fast as they can and hit like a truck. This is to injure/disable the prey and make it safer to feed on. In this process they find out exactly what there prey is and often if its not what they were after its left alone (obviously this is there "normal" modis operandi and nto always what happens).
2nd: Tigers and Bull Sharks.
These guys are bad. A big Tiger (and they do get well over 5M and 1500kg) WILL eat ANYTHING. they have been found with number plates, rain coats, deer, humans big turtles and a multitude of other items in their stomachs that would not always be considered normal food for a shark, on top of this they are quite fearless compared to whites and will attack anytime and will chase you to the point off beaching themself (very shallow water).
Bulls are probably the worst. They do get big although nowhere near the size of tiger or whites. The real danger with these guys if they love many of the places we swim (river mouths, cannals, creeks) and are also quite fearless. they can live in fresh water hundreds of kms from the ocean and as the water is often dirty they bite just to find out what you are. They often attach in groups and even when they know you are not a fish they will eat you anyway.
Last! Stats: Its all well and good to quote stats saying your more likely to get killed by lightening but put it in context. In you constantly play golf or stay out on your pole board (or kite probably) in an electical storm sooner or later you WILL get hit. If you swim in the same spot for 18 years at the same time you WILL run into a shark. Its RELATIVE EXPOSURE, we as water people are far more likely to encounter sharks, sting rays, stone fish, jelly fish then anyone else and the more you are out there the more likely it is you will have trouble at some time.
I have been surfin since 5, sailboarding since 10, scuba since 18 and kiting for the last 3 years (31 years on/in the water). I have been stung many time by jellies, stood on a few sting rays without incident luckely, found a big stone fish right where a bunch of us were walking in and out of the water to kite and been attach by a nine foot bronze whaler of birubi pt near Newcastle.
I still get out there every chance I can but I am cautious about dusk, I drag my feet across sand rather then stomp along in murky water, If fish/ other sea creature are acting weird or I see a big shark I am out of there!
Almost every one I know with the same sort of time on the water will have the scars to prove it or a very close call story.
AHHHHH thats it I am done. Dont stop kiddies, its fun just repect what is around you and dont assume it cant happen to you.