In case you haven't heard, IE8 is out in Beta form. I've downloaded it, and life has not ended. Yes, a few sites have had rendering issues. Some sites have told me that I don't have a browser they support - but this has rarely happened. Usually, worst case is that I click on the "Emulate IE7" button and keep moving on.
Why would I run IE8 on my every day machine:
Resources to learn more about IE8:
I haven't seen an expected RTM date (actually, I should say RTW), but it doesn't appear to be anytime soon.