Well, maybe in my setup or brain.
I just installed WP2.0 over a WP1.5 site and it wen without a hitch.
If I bring up an existing post in the wysiwyg editor and do nothing except 'Save' the result is a garbaged post
The post has an image and it appears that multiple partial copies of the image code have been strewn through the code.
The wysiwyg editor screen looks ok. The wysiwyg preview shows no image.
The text editor works fine, but I sure could use the wysiwyg!