After 3 years of work, Guile 2.0.0 was released on February 16, 2011. I have it up and running on my iMac and it appears to be an excellent Scheme implementation. It has a new compiler and associated VM that work seamlessly. See the News file for a list of all the new goodies.
The Gentoo port isn't out yet and I don't use any of the Mac package handlers so I had to build it from scratch. That wouldn't be difficult except that many of the necessary libraries are missing on the Mac. I'll write up and post some notes on how to get it running on the Mac. Other systems will be similar but probably easier. If you're willing to wait for the packages, it should be a breeze.