ACS was originally at 4.2. If you want to avoid confusion I would make it 4.3. The code quality is certainly much better than 4.2 ever was.
Even though it is labeled alpha, I am using OpenACS on many sites (albeit none with a huge user base) because I feel that it really is more stable than 4.2.
Can we just come to an agreement such as: starting with the beta release, all the core of OpenACS will not break the data model without an associated upgrade script.
As for packages that aren't part of the core, make the same rule. Beta and beyond won't break the data model. Of course, you can add the upgrade scripts at any time before that and that would be even better.
