It's pretty buggy. Lots of stuff coded purely to standards and not to a particular browser isn't rendering correctly. All in all though, that's expected, this is not the final product, they're still hammering away on some pretty big things.
Temperatures plummeted to new record lows in hell today on the recent news of an about-face to IE8's standards mode default. If you haven't been living under a rock, I'm talking about the recent news that IE8 will, in fact, by default, act like IE8.
I used to think that "em" units were the bee's knees. The cat's meow. The way it should be done.
Then I encountered weird bugs and design glitches and spent hours trying to figure out how to fix them. IE 5.5 was a real bear to whip into submission. IE 6.0 has some trouble with em units too.