var saving = false;
var saveagain = false;
var savetimer = null;
var saveInterval = 15000; // ms save interval
function save() {
  if (saving = true) {
    saveagain = true;
    return;
  }
  saving = true;
  clearTimeout(savetimer);
  save_internal();
}
function save_internal() {
   /* ajax call here w/ callback being passed as save_response */
}
function save_response() {
  /* code to evaluate save succeeded or not */
  if (saveagain) {
    saveagain = false;
    save_internal();
  } else {
    save_startTimer();
  }
}
function save_startTimer() {
  if (savetimer) {
    return; // save already queued
  }
  savetimer = setTimeout('save()', saveInterval);
}
function setUserChoice() {
  /* code here to set user selection */
  save_startTimer();
}