Holy crap, I was just thinking of posting some stuff about IE8 and this article came across my /. RSS feed which sums up all the Betas fairly nicely:
http://technologizer.com/2008/12/04/state-of-the-browser-betas-a-technologizer-cheat-sheet/
http://tech.slashdot.org/article.pl?sid=08/12/05/218208
Hah! Sometimes /. comments have interesting tidbits in them, like did you know that
Opera 10 alpha aces Acid3 browser test and adds 30% performance?
http://www.computerworld.com/action/article.do?command=viewArticleBasic&articleId=9122719&intsrc=news_ts_head
Cos I didn't!
Just be sure its actually implementing the bits it says its passing ;) Opera has a habit of stubbing out bits just so it passes in Acid, and then fills them in later.