Here's an idea I've seen in a couple of places recently: that because people are living so much longer, and are so much healthier at more advanced ages than in the past, they're more likely to continue working past the traditional age of retirement.

Marvin Olasky: The best Social Security: Work:

"Today, though, with improved health care, most people make it to 65 (or 66, scheduled to be the vesting age for most baby boomers) fit as only a slightly dented fiddle."

I wonder if there's any way to take that into account in the quantitative examinations of Social Security's future.