Assets (illustrations and examples) are now retina-ready. Too bad this is for the documentation pages only and doesn't include bundled icons. :( http://twitter.github.com/bootstrap/base-css.html#icons
Bootstrap was going to ditch Glyphicons (and IE7 support) with 2.2.2[1] but it looks like they're either holding off on that or they changed their mind. I recommend using Font Awesome[2] instead of Glyphicons. [1] http://blog.getbootstrap.com/2012/11/09/glyphicons-font/ [2] http://fortawesome.github.com/Font-Awesome/
You can also use http://retinajs.com/ to scale stuff up if you want.