Great insight on interest rates, and how low they are likely to go.

Informative article about how mortgage rates are structured using coupons

How low can interest rates go?

From just skimming it looks like the lowest a 30 year mortgage can go right now is 2.75, with the possibility of 2.25, but that would be with a very bleak outlook of our future, and mentions a 1.75 but is impossible at this time.