ZDNet have an interesting article on some points that beta testers should know - the juicy bits start on page 2:
Read more in this blog post.Things have changed. According to Thurrott, “The real problem here is that the feature set of Windows 7 was frozen well before the Beta release. So the feedback [Sinofsky] discusses throughout this post is 99 percent bug testing, really (and 1 percent, we hear your concerns but have a million reasons why we can’t change a thing).”
And this is a problem? I don’t think it’s any accident that the two most troublesome releases in the history of Windows also had the longest beta cycles. I was running pre-beta builds of Windows 95 in 1993, nearly two years before it was released. The first alpha releases of Longhorn, which eventually became Windows Vista, were handed out at the PDC in late 2003, nearly three years before Vista shipped.