A thought about health care availability for those with preexisting conditions that prevent obtaining insurance on the open market.
Under current law, health care insurance will be available without medical underwriting as of Jan 1, 2014. Backing that up by 18 months (typical COBRA eligibility period) would give a retirement date of July 1, 2012.
Since you've already made "your number", that could be "your date".
FWIW, I expect the labor force participation rate may just drop somewhat dramatically right around then, as many who are only working for the insurance can finally get off the treadmill.