RE: How often do you restring your bow?
I would say that if you only do a moderate amount of shooting, every two years. If are out there pounding outa couplehundred arrows a week, strings aren't going to last even a year. Regular waxing of the string, along with regular inspection for fraying, is part of the deal. And, when in doubt, change it. Do all of them - string and cables - at the same time.
I like to replace strings almost immediately, since the factory strings are almost never as good as a quality string like Winner's Choice or Bucknasty strings/cables.