I usually don't post personal finance-ish stuff, but this is a pretty good video (about 6 minutes) from Vanguard (I have an account there, though I've not really looked into retirement stuff very intensively). The guy isn't the most engaging speaker but ... you can't have everything.
What struck me is that part of the calculation of Roth IRAs is that it's usually a bet on being in a higher tax bracket when you're in retirement. Considering the amount of money that the US is spending (has spent!) on wars (Iraq, Afghanistan, on Drugs, on Terror), bank bailouts, economic stimulus and in general spending-money-we-don't-have-and-must-borrow-from-the-rest-of-the-world....
Some recent related readings that have struck a chord (all NY Times):
Not that I ever dream of being in one of those higher tax brackets mostly talked about in those two links, but I imagine that in general taxes will rise as the U.S. struggles to pay down (hahahahahaha) the national debt.