To be honest? Hardly ever, haha.
Make sure you store your buggy on a set of tires or a box or something to lift the tires off the ground, and that will stop the arms from warping. Other than that, the arms will last a long time. You have to put some serious effort into breaking one!
Suspension squeak is often from dirt in the hinge pins. Take the pins out, clean them, use a pipe cleaner in the holes in the arm and the pivot blocks, and the squeak should go away.