The 20% sounds very alluring, but you have to ponder whether it's sustainable. The old "rule of 72" applied here means we'd double our money every 3 1/2 years, give or take. In a world of all other things being equal, that would mean you could put in $1,000 when you're 21 years old, leave it alone till you're just shy of 60 and have a little over a million.

I know this may be the "age of abundance," but I have a sneaking suspicion that greater society would have pretty rampant inflation for a 20% ROI to be sustainable in the long term.