Some of my blogs are missing the buttons in the "Visual" side of the post/page editor. This happened during one of the upgrades to 5.5. Currently I am running several on beta 10.
The weird thing is at least one of my 5.5 beta 10 semiologic blogs is ok - but others are missing the buttons (they appear as blank boxes).
All are installed on the same server. All have been upgraded using the Semiologic Pro upgrade wizard at least a few times. I think all have the same plugins enabled.
Looks like I fixed the problem by manually re-uploading tinymce. Must have been corrupted uploads - probably happened during one of the wizard upgrades.