Prepaying your mortgage is almost always a bad idea. Mortgage rates are generally pretty low and mortgage interest is tax deductible. If you got extra money each month, you should first pay off any outstanding debt, then sock away 3-6 months worth of expenses in CDs or a Money Market or something similar. Once that's done, I'd suggest sticking the money in a Roth IRA. By paying ahead on your mortgage, you're basically putting all your eggs in one basket — your home equity. Should something happen, there's a good chance that you might not be able to access that equity or you might lose it altogether. Paying ahead on the mortgage can have a lot of emotional satisfaction, but it's a poor use of your financial resources.

Chuchundra, Your comment is correct, but I was trying to show that you can prepay your mortgage yourself at no cost without having to pay a fee to a service which makes the additional payments.