This system has mostly been designed and implemented It works and is usable. For example, these web pages have been rendered on a GNU/Hurd system.
You can try it out for yourself: for getting access, installing Debian GNU/Hurd will probably be the easiest and most feature-complete solution. If you don’t have spare hardware to use for doing so, you can also get a shell account on a public Hurd machine. Depending on the things you’re going to work on (and on your internet connection), this may be an easy way of getting used to Hurd systems. Installing in a virtual machine is another possibility, see the page about running a Hurd system for the full story. In particular, running a Debian GNU/Hurd QEMU image may be a viable alternative.
it is mostly based on the same sources. It is not an official Debian release, but it is an official Debian GNU/Hurd port release.