Now that I am in my 5th year of retirement, I would not return to work even for a day for $1,000,000. ... YMMV and probably does.
Only you can speak for yourself, but I believe almost everyone would work an additional day for $1M. If nothing else, it could be a "volunteer day" with the money given to charity. But I accept your point.
And it is a fascinating question.
When I joined this forum in January 2007 (same day as W2R, BTW), my targeted retirement date was November of 2009, with an absolute upper limit retirement date set for November of 2012. Not a second longer. Done deal. Guaranteed. No question. Positively. Beyond a shadow of a doubt. But here it is 2014 and I'm still working at age 54.
I do not make a million dollars a year but I make close to $500K/yr when my salary and the increase in the capitalized value of my pension are combined. This is a lot to give up. It does not matter that I do not need the money. It is still a lot to give up. I did not think this way five years ago. But it is different now that the ramifications are real. Once I leave, there is no turning back.
And my job comes at a price. I work 60-70 hours/week. The work itself isn't particularly difficult (e.g., limited travel, jeans and t-shirts in the office), but it is extremely stressful. Fortunately, it is not as bad as it was 7-8 years ago. This is probably because I and everyone else knows that I can walk out the door at any time. But it is still stressful. And there is the loss of freedom. Work makes it more difficult to pursue some activities. No six month backpacking trips.
But freedom goes both ways. There is significant financial freedom knowing that my needs and the needs of those around me can be met. For example, people talk a lot about LTC insurance and nursing home costs of $100K/yr. I do not think much about this. If my mother and/or my step-mother needs to spend three years in a nursing home, I can take care of this. I do not need to worry. But maybe there will be other costs that I cannot as easily afford. So maybe I should keep working.
I may retire tomorrow (literally), but I have yet to retire today. So for me, the compensation is still too good to pass up. It isn't the money. It's the financial freedom to do anything I need (or want). It's freedom from worry.