I just updated to version 2.3. Since doing so, the bold, italic, etc, icons do not show up in the Rich Editor when writing a post. All that shows up are a couple of icons (more, spell check, and a couple of others).
I've uploaded a screen cap image so you can see the problem:
I was thinking something was wrong with the Tiny MCE image files, so I tried replacing the entire "js" directory within the wp-includes directory. But that didn't work.