Buried in the late-June "Bits from the Release Team" minutes is the news that the Debian Project will aim for a time-based freeze for the next stable release, Wheezy. At the moment that date is June 2012:
After some discussion at the sprint, we have looked again at the concept of having a time based freeze. I'd like to thank the DPL for progressing a consensus on debian-devel on a way forward for this proposal. The release team would like to support the idea of a time based freeze.
Its main advantage seems to be the clarity that people will get knowing when we will freeze. For this reason, we need to pick a date. This is one that not everyone will be happy with, and caused quite a bit of discussion. However, we had to make a decision, and have picked on June 2012 as the current proposed freeze date for the next release.
This means that the current Debian Testing release, which is Wheezy, is set to be frozen at that time (no new versions of packages, just bug fixes) in preparation for the next stable release.
And given the recent history of Debian releases, I think that means aiming for a February 2013 release to follow Lenny's February 2009 and Squeeze's February 2011 releases, continuing the pattern of two years between stable releases.
Add the extra year of maintenance as Old Stable, and that gives Debian releases effectively a three-year support life.
For users who aren't already running Debian Testing (and that includes me), the prospective June 2012 freeze is a good time to migrate from Stable to Testing in anticipation of Wheezy becoming Stable early in the following year.
Debian Developers in favor of the freeze have said that users appreciate the ability to plan for the future knowing roughly what will happen to the stable Debian release (in contrast to the "ready when it's ready, and that's it" way of thinking). I agree. I'm already thinking of Debian Stable in terms of the two-year release cycle, substituting newer bits from Debian Backports, the Debian Mozilla Team APT archive, Liquorix, Google and Dropbox as I need them to keep my Debian Squeeze installation a bit fresher between now and then.