First of, it's Beta 1, at least from what I can see (as coincedence has it, I just DL'ed it yesterday but it would not install on my test machine - maybe has to do with the fact that IE7 got slipstreamed instead of installed on top of IE6 and hence cannot be removed?).
But with MS, seeing as a RC is more of a Beta, logically, a Beta would be more like an Alpha, that's right!
Second, well, Eric, no, we shouldn't be responsible generally.
However, this is for all site owners that implemented some sort of non-official (according to W3C at least) fixes for IE6 and below.
IE8 will do away with the legacy mode that will render the pages like <=IE6 rather than the W3C standard and those and only those pages will be messed up since.
So, what MS is telling us is do away with your previous non-standrad workarounds to make your pages look fine on our browsers and finally stick to the standards
At least that's what I have gathered about the IE8 discussion so far