For me, half my student loans are just over 3% and half are over 12%. I'll attack the 12% ones first. As for mortgage, I am at 5%, so you're right in that it makes more sense to invest the money and just pay that loan over the life of the mortgage.
However, if you can make quite a bit in business and investing, paying off any/all loans as quick as possible gives you a sense of freedom and the reassurance that if everything you had completely tanked tomorrow, you wouldn't have to worry about writing checks every month for loans.
I suppose something where I pay good chunks off at a time and still leave ample amounts to invest is a good balance.
I'm always interested in what people do and how they do it. I am a firm believer in automated income, especially after reading The 4-Hour Work Week by Tim Ferriss. And although he makes little mention of investing other than IRA and 401K plans, I think the stock market is a good place to strive for that.