If I would have known the market was going to crash I would have kept renting instead and then could have gotten a much better deal (and much lower mortgage) after the crash.
Also, that I really didn't have to pay a bug exterminator every 3 months to come out and spray outside and inside for insects, when I could have done it myself with a $10 jug of bug spray from Home Depot and could have saved a ton of money.
Also, I really didn't have to pay a landscaper every 3 months to "treat" my lawn for weeds and lime it, and they really didn't do much. I eventually started doing it myself after attending a lawn maintenance class and I did a much better job than they did with a weed and feed and a sprayer and saved a ton of money there to.
For a little while I would have invested in Angie's List to get a list of good contractors instead of some of the yahoos I had to deal with.
Well that's more than one, sorry I got carried away. Great question.