Skeleton is made to scale to also fit mobile browsers, following the principles of responsive web design. Does Bootstrap offer the same?
Not yet - http://groups.google.com/group/twitter-bootstrap/browse_thread/thread/6db57d09f654a326?pli=1
But it will be, at some point. The Roadmap has this in for version 2.0. It's lightweight enough that in my experience you can add in your own media queries
without much trouble.
EDIT - As of 1 Feb 2012, version 2.0 is out, which is responsive down to mobile out of the box.
EDIT - As of 19 Aug 2013, version 3.0 is out, which is not only responsive but takes a mobile-first approach:
With Bootstrap 2, we added optional mobile friendly styles for key aspects of the framework. With Bootstrap 3, we've rewritten the project to be mobile friendly from the start. Instead of adding on optional mobile styles, they're baked right into the core. In fact, Bootstrap is mobile first. Mobile first styles can be found throughout the entire library instead of in separate files.