The Debian release team recently announced the current status of the next Debian release Squeeze. The team just finished the work on some major parts like completing the changes to run init scripts in parallel, transition to eglibc into testing, GNOME 2.30 and KDE 4.4.3. The next big step is to make Python 2.6 the default python version for sqeeeze and based on Adam Barratt estimation this could be finished sometime in late August, and at that time to freeze the release.
Squeeze freeze was planed for December 2009, meaning it is already way behind schedule, and it looks that it is not so easy for the Debian project to switch to a fixed 2 year release cycle (or freeze cycle). This was pushed back because of the high number of critical bugs for a release freeze. Based on past experiences there will be at least 4 months needed after the freeze to release the next stable version, meaning this could show up by the end of the year if everything works out fine. But realistically, this could take 6-8 months after the freeze, and push the release date in 2011.