Just some feedback on the image uploader problems (I've read the sticky...)
In my case the image doesn't get uploaded, but after it seems that the upload was succesfull (which is actually not true and no error messages) inside the popup window strangely enough my homepage/index.php appears...
After that Firefox often just shuts down.
Ubuntu Gutsy / latest Firefox (184.108.40.206) and flash player (version 9, just en few weeks old) / fresh install of WP 2.5.
Hope this information helps in solving the problem :).