Just to echo this, I do much the same with Slackware. I use -current on some machines. Every time a release is pending, work on -current slows down (or does it ramp up?) and it is stablised.

It's essentially a development release rather than being explicitly labelled "rolling" (and, in fact, its use as a day-to-day distribution is generally considered A Bad Thing if you're not a Slackware developer/tester). It just happens to have the bonus of also being a pretty bleeding-edge, yet stable rolling release.

So, it's possible to achieve both a rolling release and "stable", versioned releases.