Since I last wrote about pre-paying your mortgage, there has been more discussion on this topic, and it's worth discussing again.
First, I'd recommend a read of Scott Burns' take on the topic, titled "Most retirees should be mortgage free". Now, I do note that the exact question he's addressing isn't about pre-paying, per se, but about whether it makes sense to have a mortgage when you retire. To me, this is a different facet of the same issue, as not many 30-year olds are buying a home they will pay off and retire in, 30 years hence. So at some point the need to pay down the mortgage needs to be addressed.
Another story just appeared in Business Week with a different view, "Pay Off the House? Not So Fast." The BW article author, Ellen Hoffman focuses on a couple who is in the 33% bracket. This would require a taxable income of $188,450 after the $41,000 she suggests they put in their 401(k) and the $24,000 in mortgage interest. Basically, she focused on a couple making $250,000/yr, hardly typical. In Scott Burns' article, he separates retirees into three groups, "The Abundants", "The Prudents", and "The House Poors". In the end, it's only the abundants who should even consider the post retirement mortgage, and it's Ellen Hoffman's well off couple who should invest in lieu of any pre-payments.
I maintain that one's position should be carefully reviewed, as there are many variables to consider.
Is your interest completely deductible? i.e. have you other deductions which exceed the standard deduction?
What is your tax bracket, and therefore, what is your after tax cost of borrowing?
For Ms Hoffman's example, a 6% mortgage and 33% bracket, if all is deductible, yields a 4% net cost. How confidant are you that you will get a greater return than 4.7% (the amount needed to yield 4% after long term cap gains are paid) over the remaining term of your loan?
For those who are not able to fully able to deduct the interest, the true cost may be closer to the mortgage rate, and the decision to pay the mortgage off sooner, the right one. The decision to go either way is surely not clear cut. A potential for high returns vs a guaranteed fixed return is a much repeated situation, and the basis for diversification.