We've been installing Confluene 3.0 and have made good progress, especially with using Theme Builder 3.3.4. However, somehow the Theme Builder Admin section in Admin is broken, i.e., Manage Layouts shows a blank screen, and Builder Administration shows the menu tabs with nothing under them (and the hourglass running).
You can still get to the Edit Layout menu item, but the two links in the Site Admin section fail as mentioned previously.
We just created a new Confluence instance on a different server, and (mistakenly) installed 3.3.5-M2, same problem. Then, I uninstalled 3.3.5-M2 and installed 3.3.4 as I had meant to do in the first place. Problem persists. I seem to recall that Manage and Admin used to work in 3.3.4. If that was so, then perhaps installing 3.3.5-M2 the first time caused some kind of "permanent" problem that persists even after it's un-installed
I recently noticed an Issue by Herman Boer where he describes the same thing after installing an M version, if that's any help.