How I mix Debian testing, unstable and experimental
Apart from the stable Debian Sarge, I'm now using Debian testing/unstable for my desktop. After the latest adventures in SuSEland, what could be more thrilling? (Nothing, except for Gentoo Stage 1 or Linux From Scratch.)
Using Debian Etch (testing) is not for the typical user of SuSE, Mandriva, or PCLOS. But it's much easier to get things fixed than in Slackware, and it's definitely a way to (apt-)get binary packages of almost anything, no compile time needed.
While Debian 'testing' is rather stable, it's not a release per se, but a living version of Debian. Therefore, when a package migrates from 'unstable' to 'testing', nobody could really guarantee you will be able to install it on your own Debian testing machine with all the dependencies met!
That's why you will occasionally have to met dependencies from 'unstable'. (Maybe this is the reason for /etc/debian_version to state: testing/unstable).
But this is also the reason this shouldn't be done with a production server, unless you can physically be close to the server to fix problems, should they arise.
One you accepted to use Debian testing/unstable, why shouldn't you be able to use 'experimental' repositories as well? Only with selected packages, of course, like the latest GIMP 2.3.x
The whole idea is actually explained in the manual, but let's make it simpler.