I am completely Debt free, no car loans, house paid off, no student loans, at 31. My wife and I could both leave our jobs and live for 3 years on our liquid savings without any life style changes, considering we have no large commitments.
Paying off debts is all about security, yeah I could've probably gotten a better return if I had invested my over payment. But now I invest a far higher percentage of my income than I would've while still carrying a mortgage, so I think at the end of the day I think I net out better.
To payoff the house, I bought a house I could pay off in 2 years (then I sold it and got a bigger one I could pay off in 2 years with that down payment). It was pretty easy to stay focused on overpaying just for two years. Haven't had a car payment since I was ~23, so that helped when paying off the house. Basically I sacrifice stuff that really doesn't matter much to me, for example cable, drinking, new cars, gadgets, etc. I do a monthly budget, which gives me an opportunity to really evaluate what I spend money on. I never sacrificed retirement savings though.
Now that it is all paid off, I have more free cash flow than I know what to do with. This year I am going to Disney World, going on a cruise, going to Maui and doing another cruise, paying cash for everything.
It does help that my wife and I are both engineers and live in a low cost of living area, but I know people who make far more than us that are in debt to their eyeballs because they can't control their spending.