How much money is enough?

Obviously this blog has my target of $50 million in 2011 dollars ($90 million at 2031) and after that point I'm free to do whatever I like (which will probably involve lying on a beach in some sunny climate)

I asked around my office (which, as a BB investment bank is probably not representative of the general population) and the general consensus was $5 million - $15 million as walk away money (though note that typically the younger the person asked the higher the number)

However after reading the attached post on Wall Street Oasis and couldn't help but wonder how many people who reached their target number would actually retire to enjoy it.

http://www.wallstreetoasis.com/forums/john-paulson-a-one-hit-wonder-or-a-hedge-fund-god

Maybe once you start making the money it is too tempting to stop?