Brakes squeak, if you're just barely applying them, there's friction there and that's what is causing it. It's not a GSXR only problem. On cars, it's usually because the pad is worn down and there is a little metal thing that sticks out to scrape on your rotor to let you know it's time to replace your brake pads. Either you're just barely dragging the brake when it squeaks, or your pads are worn out, or there could be dirt in them like pooteeytang said.
Its not always riding the brakes, or a worn brake pad..Suzuki intruders have a nasty brake squeeeeel no mater how fresh the pads are.
That squeek is sometimes just a frequency vibration of the pad on the caliper. sometimes you can back it with a material that cuts the vibration. I've heard of using a high temp. grease, but i didn't look into it (my brakes don't squeek :neener )