I've started work on a new side-project called Fetch. It's a stand-alone CSS querying engine, designed to be super lightweight and offer high performance across all modern browsers.
It's definitely not ready for production use, but when it is, it will become the new CSS querying engine for Gimme and will also be available as a stand-alone library, which will be extensible (so you can add your own rules) and which will also be guaranteed to play nicely with other libraries by not adding to the prototype of any native objects and only introducing one single global variable (fetch).
For anyone interested, the current (i.e. sloppy) source is available on CodePlex: fetch.js.
As I said, it's not ready for prime time and the code is sloppy (and probably buggy). Consider yourself warned.