After installing WP3.0.1 I noticed that something is wrong with left side menu arrow-buttons (on admin page), also the image uploader didn’t appear as pop-up but in the left top corner on the same window. It crunched images without adding them to the post.
Things got fixed after some changes in PHP-settings by my hosting service support.
Here is what they changed in server settings:
zend engine 1 compatibility mode off
register globals off