Brad -

In my experience with web apps - alpha's are really early stage concepts meant to illustrate a concept or feature in a live web setting. Private beta's are meant as the first working release while public beta's are meant as often short term, fix the bugs and test scaling in public (goog is the one violating this rule not the other way around). And the reality is that public betas are dying in my view so what's really bullshit are public betas as the private beta is to me true to the way the term was used in the good old software days (limited release, constant revisions, etc.)