Generally, it's a bit risky to jump into a new release the very minute it comes out, usually safer to wait 1 month, especially if it's your primary or only machine.
So... 6 months between releases (sometimes nearer 7), and 9 months of support, so there's now going to be only a 2 month window in which we have to do an upgrade, lest we lose security patches? No chance to skip a version, even when something (eg the initial GNOME3 release) turns out half-baked
I do hope that they will keep critical patches going for 18 months, at least for anything that could have a remote-root type hole.
Rapid (or rolling) releases are basically a great idea because it means that when the end-users find bugs, they are reporting new bugs rather than ones that are already fixed upstream, and they benefit from the fixes. It significantly reduces maintenance work, and means everyone benefits from the latest features. BUT, it is going to need some rather careful management, so that another radical change (eg GNOME2->GNOME3, or PulseAudio, or KDE4), isn't bundled onto unsuspecting users alongside the updates they expect (eg bugfixes in coreutils, the latest firefox, or a python point-release).