Here's my take on this issue, and I've had this discussion with some people on IRC as well and for the most part I think people will disagree with me.
But they are wrong ;-) I'm actually against mixing testing and stable branches. Here's why. People choose "stable" because they are under the impression that it's somehow "safer" or "less troublesome" than "testing" (or what some people call "unstable"). I'm not so sure I agree but that's not my argument. My argument is when these people go and then try to get the "best of both worlds" by inter-marrying the branches. From my experience these people end up with less stable systems than choosing either "stable" or "testing". The problem is that they are mixing software that were not tested or intended to run with each other. And they come into problems even people in the so-called "unstable" branch don't experience. Recent examples include Xorg and GNOME updates. So these people, and the majority of them are newbies, come to think Gentoo is flaky but it's really their behavior. Unfortunately the Official Handbook tends to encourage this behavior. In theory this should be fine, but in practice it seems to produce less-stable-than-unstable software setups, so I try to discourage people from doing so. Then they laugh at me. But I've been in unstable forever. I never use the stable branch (except for testing ironically) and I remember the days when there was no distinction between stable/testing. Few times I've had problems with an update and the solution is always simple: downgrade the package in question. When I had problems with the cups upgrade, I simply reported a bug and downgraded cups. When I had a problem with findutils, I simply CC'ed myself on the bug and keyworded findutils to stable. To me that's been a lot easier than trying to figure out how to get stable package A and unstable package B to agree on inter-operability/configuration/dependencies/etc. So my advice is: pick and branch and stick with your own kind. It's far fewer headaches in the long run. And "unstable" isn't really unstable, it's "untested". There's a difference.
