When Good Debt Goes Bad...

So right now, my wife and I are trying to pay off some "bad" debt, before we start rapidly accumulating post-tax investment capital. What's interesting is that the tax deductibility of the debt makes a HUGE difference in whether debt is good or bad....

Here's a run-down of our debt:
1. Mortgage debt, 30 year fixed rate at 5.75%, this works out to an after-tax return of around 4%. Bloggers and "financial gurus" who tell you to pay down your mortgage at these interest rates are fools. We could earn a better rate of return on a treasury bond (almost), plus the mortgage allows us to enjoy a great return on the leveraged appreciation of the house.
2. Ultra-low interest federal student loans- Always be suspicious if someone tells you they need to borrow money to pay down federal student loans, as these are usually ultra-low interest rates, but are one of the few loans which survive bankruptcy.
3. Second Mortgage at 8%- While this is pretty high, it is tax deductible, so it is lower than the long-run return on the market, though many would jump at the chance to earn a guaranteed 8%. I will probably split my money between the market and paying this loan down.
4. Private Student Loans at 7.035%. The thing to note here is that because of taxes these student loans are actually higher than the second mortgage. The non-deductible 7.035% is equivalent to a market return of 11.5%. A guaranteed no-brainer.