We've been very informal in the past, as we've been a very small and intimate project in the past. We're starting to get more formal. Submitting patches via the SDM is definitely the right way to go. For the OpenACS 3x series we'll just be doing maintenance releases, so can probably live with a beta then production series (i.e. don't really need alpha).
We're careful about CVS commits so in the past, at least, the latest CVS tree has typically been more reliable than the latest production release.
I expect us to be a bit more formal about OpenACS 4 rollouts when we get there. For one thing, OpenACS 4 is much more complex than OpenACS 3.2, and testing is intrinsically more complex due to our support of (currently) two rather than just one RDBMS. The project's also larger and growing in terms of people doing work, and the larger a project gets the less likely that an informal approach will work well.
