Allright, I'm trying the new editor right now. It's got a lot of improved features. Hand-coding your posts is the way to go normally, but there's always the time factor. I'm not goint to use the Compose option anytime, I don't trust automated WYSIWYG editors to do their jobs. But the Edit HTML section is nicely improved. And as far as I can tell, this editor is XHTML 1.0 compliant.
There's bound to be a few quirks with this for the time being. I don't recommend editing old posts with this anytime toon.