I think the navigation works fine. I would very highly recommend not using web-fonts for anything less than 16 points unless it is a very high quality font specifically designed for smaller sizes on the web. The hinting on Quicksand at smaller sizes is absolutely atrocious, and while it is going to appear ok on some screens and at certain resolutions, there will be some devices that it will be almost illegible on.
This is the second website someone has posted in the last couple of days using Quicksand. It is a nice looking font, but is not truly web ready. If you must go with a free font, you might want to look at Dosis. At thinner it weights it is far superior to Quicksand. Droid Sans, Source Sans Pro, Lato, PT Sans, and Proxima Nova, are other possibilities.