My good friend has worked at ups for 6 and 1/2 years now. After his 2 year mark he left UPS and went to work fulltime at a another shipping company. Decided 6 months into that job that he hated it and wanted to come back. So he came back and talked with our HR lady and they brought him back literally the next day. Now here is were things get a little crazy. He was brought back and they let him keep his hire date, seniority, and his pay as well as all his time off etc... keep in mind he quit and didn't work there for a half a year yet he kept that 2 years vested as if he never left. This happened once and is the only case I know of but still it happened. I doubt in today's economy you could get the same deal but it is definitely worth a shot.