With $20MM in the bank, there is plenty you cannot buy and subsequently maintain for very long: a shiny new Bombardier jet, a motor yacht, more than one vintage racing Ferrari... even blowing $5MM on a substantial estate would be highly ill-advised. But at this point, one becomes acquainted with people who can afford to keep such things, so it might start to seem less like "wealth" and more like "security" depending on one's desires and insecurities.

Consumption of ultra-luxury items is one way to look at the difference, but another is your progeny. $20M, if spent frugally and invested well, could certainly ensure the well-being of your immediate children and probably grandchildren as well (not if you blow it on vintage sports cars and jets, though). But a billion or two could keep your family out of work for many, many generations

Why is keeping your family out of work for many generations a good thing?

It's not: http://www.theatlantic.com/magazine/print/2011/04/secret-fea...

I wish my grandparents had left me a few million dollars.

Keeping your family out of work is not the same as giving them the option of not working.

If you put it in a mattress, sure.

But most (all?) people invest their money at a far higher rate of return than inflation.

Not for a decade or more has this been true. Inflation in the UK is 2.2%. You would be lucky to get that without venturing into equities (which to be fair have done well this year) or property. But energy is up 8%, travel 9%, food 12%, etc. Real inflation is hard to outrun. And markets are prone to bubbles...

My intent was to put $20MM or so in perspective: yes, prudent investment could put such an amount to good, long-term use, but it is not so much money that it would be challenging to spend it all within a decade or so. $1Bn is something else entirely, and would require a very concerted effort to squander quickly.

You could pay for your $5 million estate in cash with the dividends from a 'boring' investment in AT&T's stock (5.1% dividend) after six years, while never touching the principle.

20$ million is barely anything if you want to actually make a difference, as opposed to just surviving without having to work.