No, IE8 pretty much is compliant. The only issues I've been having with the beta is that the old IE6/7 hacks break the renderer. Not too surprising, really.
Windows Update, unfortunately, doesn't play nicely with IE8 yet (I have to set it to IE7 emulation mode to use it). Not a big deal, really...it'll work fine by the time the final release comes out. Also, that's only a real big deal with my laptop, which still runs XP MCE.