Since upgrading to Wordpress 2.6 I noticed the Add Media buttons appear to be missing and in fullscreen mode are greyed out. The lack of 'Add an Image' and 'Add Video' buttons make it much harder for adding pictures and youtube videos to your blog posts and pages.
A quick fix for this is to install the following Wordpress plugin TinyMCE Advanced by Andrew Ozz. This plugin will give you easy image adding and many other customizable features.
"This plugin adds 15 plugins to TinyMCE: Advanced hr, Advanced Image, Advanced Link, Context Menu, Emotions (Smilies), Date and Time, IESpell, Layer, Nonbreaking, Print, Search and Replace, Style, Table, Visual Characters and XHTML Extras."