With Google forms, responses are saved into a spreadsheet. You may want to remove some or all responses, but there's no form API that allows that. This gist contains a function that can remove some or all responses, starting with the first (oldest) one. This works with the legacy forms product (pre-February 2013). This was written in response to…

TidyGoogleFormResponses.js

/**
 * Delete form response rows. If no input parameter is provided, prompt user
 * for the number of form response rows to remove. To remove all rows, input
 * -1.
 *
 * Assumes that the form responses are in the active sheet, that there is one
 * row of 'headers' followed by responses (starting in row 2).
 *
 * @param {number} thisMany (Optional) The number of rows to remove. If not
 *                          specified, user will be prompted for input.
 */
function tidy(thisMany) {
  if (tidy.arguments.length == 0) {
    thisMany = Browser.inputBox("How many responses should be tidied? (-1 for all)");
  }

  var sheet = SpreadsheetApp.getActiveSheet();

  
  if (thisMany == -1) {
    thisMany = sheet.getDataRange().getNumRows() - 1;
  }

  if (thisMany == 0) {
    // Nothing to do
    return;
  }
  else {
    // Delete thisMany rows, starting in row 2.
    sheet.deleteRows(2, thisMany);
  }
}