These breakpoints seem chosen somewhat arbitrarily. I'd enjoy a longer post elaborating on why you chose them!

The seminal Boston Globe design chose 5 breakpoints based on rough hardware buckets, see http://www.flickr.com/photos/joshclark/6200745034/ (via https://twitter.com/globalmoxie/status/120157487797243905 ).

It irritates me to see how people simply rip off Dustin Curtis' SVBTLE layout. This is disgusting.