Some where on here a detailed why it does and how to fix it(with pictures to) is a really good thread, I have to leave the house for a while so hopefully some one can post the link.
In short you remove your tank from the bike, remove the sender float unit which has the fuel filter and pump attached to it, hook up an electrical meter and bend the rod until a certain reading occurrs or something like that.
Mines comes on at around 85miles never gave it a second thought but when I replace my fuel filter I will try and correct it.