On 08 and 09 bikes, if you look at the space around the outside of keyholder at the 9:00 position, you can see a little square tab sticking out from the keyswitch over a little square plastic plunger in a plastic square hole. When the key is pushed in, that tab pushes on the plunger. in a plastic square hole. The plunger has a spring inside of it that looks like it came out of a ball point pen and the switch is under the plunger. The switch never goes out, it is the plunger sticking. The plunger and hole is pretty long and pretty tight clearance, so over time dirt builds up and the plunger sticks in the bottom position holding the switch down and the bike will not start (that is why some people bang on it, to make the plunger pop back up). Squirting a cleaner around the plunger that is plastic save is a good way to clean it out and let the plunger come back up. Cleaning it every once in a while and you would prabably never have a problem with it.
Kawasaki will install the newer stronger spring for free through the dealers, but it is not simple to do, make sure you get them to order the new security bolts before they start, as the bolts are one time use only to prevent theft. The newer bikes also have a splash shield in that space where you can see the tab and plunger/hole to try to keep it cleaner.