2-3 Mill at a 5% annual return is fine for most of us to live comfortably on, but the problem is that you never know what's going to happen to the currency itself.
A lot of inflation is a GIVEN over 20 or 30 years, so that 3 million WILL act more like 1 million to your purchases after that time. So that in itself sucks and you really need to be re-investing some of your monthly dividends back into the principle just to beat inflation.
Then there is the threat of the USD hyperinflating when we hit our debt wall. $3 Million USD might not be able to buy you some starbucks when that happens, all because Nixon took us off the gold standard and washington can't balance it's freaking checkbook.
So to combat this issue, I'd recommend keeping multiple funds in multiple currencies. Look at the top innovating countries of the day and put a million dollar fund in their currency, each, if you want the best results.
China's RMB is the obvious one going up right now, but Japan is no slouch and frankly whatever currency Germany uses this week is always going to be a good safe bet... If you be sure and switch with them when they jump off the euro.

Canada, Thailand, Oz, NZ, there are many strong countries out there that aren't going to take the nosedive with us and may even profit off the USD's demise... So be sure you're balanced between a few for any such long term plan.
...And a few precious metals don't hurt too.
