This is a 0.5 release because there's a lot left to do. There are tons of packages left to write in order to have a good selection of free software. We would love some help.
>Is Firefox even in? (no. Icecat is, whatever that is. Don't ask if Chrome is in.)
GNU Icecat is a fork of Firefox with the nonfree bits removed. Chrome is proprietary so it will absolutely not be part of the GNU distribution. Chromium has licensing issues (and is a nightmare to package, btw: https://twitter.com/spotrh/status/410479218791706624). I don't know of any fully free distro that packages it so I don't think it will be available in Guix.
However, if you do want to use proprietary software, you could always pull packages from other sources that package such things.
Honestly, the first one (of Nix vs. Guix) that can replace dpkg on my (non-NixOS) system is welcome! For now, having this "unstable" in the default nix channel (http://nixos.org/channels/nixpkgs-unstable) is scary.
Also, the selection of packages in Guix is way too small. 600 advertized, vs. nearly 10000 for nix. Is Firefox even in? (no. Icecat is, whatever that is. Don't ask if Chrome is in.)
Another thing: Guix seems to default to per-user package installation, unlike Nix. http://xkcd.com/1200/ comes to mind. In the case of Nix, "you can steal my cookies, but you cannot list Nix packages I can install!"