Put the money toward your investments and let them grow.

By 2010, your mortgage balance to refinance will be smaller. Your house value will be bigger. Your LTV ratio will be way low, which is good - you will probably get a good refinance rate. Or you may choose to move between now and then.

Either way, go for the growth in your retirement savings.

This assumes that you have adequate emergency funds. Consider this: if you have a short-term cash flow problem, it's easy to extract $ from savings or from liquid investments. If you paid ahead on your mortgage, the only way to get that cash back is to sell your home or to get a home equity loan, both of which take time and have fees involved.

SubGuy