I have found three potentially annoying bugs in 2.6.3....
In the Visual tab of the text editor, none of the information on the buttons show up. The buttons show up but you can only tell what they do by the tool tips that pop up.
I have all of my pop3 information right but when i run wp-mail.php i just get a blank error....POP3 connect: Error  ..... and my posts do not get posted.
I just happened to click on plugin editor and i get an error 404 even when the file is there.
I don't understand why people don't test everything before they release it. This is only my second day and I've already found three bugs.