Update: I can not recommend the usage of this plugin any more.
I was anxious to finally try out the wordpress 2.7 beta. As a happy user of Ozh's admin drop down menu I had to realize that the menus were completely gone in the backend.
I was a little surprised, I guess more plugins will break. A fix, of course, is to simply remove ozh-admin-drop-down-menu from your wordpress/wp-content/plugins/ folder.
One of the things Ozh's menu does is to look for the #adminmenu list and hide it. I'm not sure who's the culprit here, the wordpress developers for not renaming their css class while doing such fundamental changes or Ozh for not checking the wordpress version. Well, it's still a beta and maybe someone will include a better fix.
The new admin menu is kind of neat, but I think Ozh's menu is far superior. We'll see if Ozh changes his mind.
Update: The plugin has been updated and works fine in 2.7 now. I liked the old look better, but the improved usability and speed is what matters most to me.