The (Rails) application in question is an internal application and the audience uses modern browsers on various operating systems (FireFox 4, Safari 5, Chrome 10 and IE 9). No need to care about all the old browsers.
Are there any serious (upcoming) grid or fluid frameworks you can recommend despite the well-known Blueprint and 960?
1140px is an interesting one I’ve been using recently, it’s designed to work well on high resolution monitors and degrade nicely on much lower resolution monitors (like phones, tablets, etc). http://cssgrid.net/