Kraken-Sass works on all modern browsers, and IE 8 and above.
Because IE 8 and lower do not recognize media queries, they will receive the single-column mobile layout instead of the fluid grid. (Learn how to add media query "support" for older browsers.)
Also, rounded corners, gradients and drop-shadows on things like buttons and forms aren't recognized by IE 8 and lower and some mobile browsers (like Opera Mini). Forms and buttons still work in those browsers - they just look a bit simpler.