For us (an end user who occasionaly develops for others) the concept of a six monthly update that does not have backward compatiblity is one of the biggest worries in using Drupal. While I understand the ideal and applaud it, it does bring up the issue of leverage in regard to the financial investment made.
We want to see a return on any investment we make so having to start an upgrade cycle every six months if going to be very hard to justify especially as the size of our sites mean that we are going to be constantly programming to stay still. Our most recent project has had over 400 man days in development and uses a huge number of contributed modules to update to V5 is going to be a major task.
The way I see it is:
V5 - released e.g. Nov 1
V5 - Reasonably stable - Dec 1
Most Key Contrib modules V5 ready Feb 1
3 Months testing and migrating = April 1
Next Version of Drupal due for release = April 1
We are thinking of skipping every 2nd version as a 1 yearly cycle may be achievable, but it is worrying that the release cycle is less that the time it takes to develop any decent size of site. Essentially the release cycle is inline with Fedora Style of release but fedora is not patently not suitable for large scale use and is a testing ground for new features that subsequently get put into enterprise ready releases.
I am guessing that a lot of people here will also have the same issue with any site that is medium to large in size, what approach's are people taking to this?