Despite my warnings above, I know many readers of this document wish to run the testing or unstable suites of Debian as their main system for self-administered Desktop environments. This is because they work very well, are updated frequently, and offer the latest features.This is not a work computer (or "production machine" as they are described more grandly), I have my trusty Crunchbang Live USB handy, and I am willing to put up with a bit of pain.
!Caution For your production server, the stable suite with the security updates is recommended. The same can be said for desktop PCs on which you can spend limited administration efforts, e.g. for your mother's PC.It takes no more than simply setting the distribution string in the "/etc/apt/sources.list" to the suite name: "testing" or "unstable"; or the codename: "wheezy" [now Jessie] or "sid". This makes you live the life of eternal upgrades.
The use of testing or unstable is a lot of fun but comes with some risks. Even though the unstable suite of Debian system looks very stable for most of the times, there have been some package problems on the testing and unstable suite of Debian system and a few of them were not so trivial to resolve. It may be quite painful for you. Sometimes, you may have a broken package or missing functionality for a few weeks.
I used Wheezy Testing for several months before the freeze and had no major problems, but maybe the cascade of new packages now Testing has been unfrozen will be a different experience. I'm looking forward to the fun!