maenial: as it happens that's more or less exactly what I do on my desktop: I run Branched until it goes stable, stick with it for the two months until the next branch point, and then jump to the next Branched release. I have a laptop on which I usually run stable and only jump to the next release around Beta time, though, so I have a backup for when things get real hairy.
I haven't actually used any of the popular rolling distros much (Arch, PCLOS, sid etc) so I can't honestly compare this approach to them in terms of reliability, but I suspect it's a bit less reliable. Branched is often pretty rough until Alpha release at least. For example, I bumped the desktop (this box) to F18 last week, it basically _works_ but I had to remove a few packages to make the upgrade (with yum) actually run, I had to work around a problem with polkit which made it impossible to get into GNOME after the update ('yum reinstall polkit' does the trick, for the record), and now I've fixed things up it basically works but there are some notable issues, GNOME 3.5 still has some obvious bugs at this point (Evolution in particular is so buggy it's basically unusable, and for all the Evo haters out there, I actually usually find Evolution pleasant, so that's not 'just normal' :>). So you can do this, but it's not going to be entirely smooth.
To clear up your confusion regarding updates-testing: updates-testing is a repository, not a release. Every Fedora release has an updates-testing repository - so right now, Fedora 18 has one, but so does Fedora 17 and Fedora 16. It doesn't make sense to say 'I want to use Branched so I'm going to update from updates-testing', that's just...not how it works
You can pretty much just approach a Branched release exactly as if it's a stable release in terms of how you actually upgrade to and maintain it: if you want to bump to the current Branched release you just have to use the repositories from that release. So right now if you want to use Fedora 18, you use the Fedora 18 repositories. It has a release repository, an updates repository and an updates-testing repository just like F16 and F17 (the current stable releases) do. There's two differences, though: the 'release' repository for a stable release is frozen, it contains the exact package set that was cut for the release and never changes. For stable releases, potential updates go first into updates-testing then move to the updates repository. For Branched, since the release isn't actually final yet, the 'updates' repository contains nothing - it's empty until release time - and potential new packages go first into 'updates-testing', and from there go, not into 'updates', but into 'release'. It's significant if you're in release engineering but doesn't matter a huge deal if you're a user, just thought I'd mention it. Turning on the 'updates' repository when you're running Branched won't hurt anything, but you'll never get any packages from it, until after the Final freeze goes into place.
I find upgrading with yum is usually the most reliable way to bump to Branched if you're going to do it before Beta, because we don't really start testing the installer-based upgrade functionality until Beta time, during Alpha time it's often broken. So just refer to https://fedoraproject.org/wiki/Upgra...dora_using_yum
. The two minute version of how to use Branched is just 'follow the instructions on the upgrading using yum page': if you do that, the repositories will be set up for you, you don't actually need to worry about them.