You're definitely not alone. I've been running Garageband 09 on Mountain Lion for weeks and it just started doing the same problem today. I tried restarting the program, tried restarting my Mac, tried updating the OS to the newest mini-update. Nothing helps. It also seems like the name of the last instrument track I was on before the problem started shows up above where the tracks should be regardless of what track is actually selected. Additionally, if I click where the options of the effects would normally trigger drop-down menus, the drop-down still works -- you just can't see them.
If you happen to find a cure, do post!
After upgrading to Mountain Lion, I found that the effets slots were invisible but by aiming carefully I could still get drop-down menus for some of the widgets that should have been there.
I was able to fix it by removing some of GarageBand's preference files.
First, close GarageBand.
Then, open your user Library folder. This is a hidden folder that normally does not appear in the Finder. The easiest way to open it is to go to the Finder and select "Go->Go to Folder..." from the menubar and type "~/Library" in the dialog box.
Once you are in your Library folder, drag the following items to the trash:
Finally, relaunch GarageBand. I found that after following these steps, the effects slots were once again visible in the track info panel.
Note that some of the files listed above may contain settings for any custom instruments that you have. It might not be necessary to delete all of those files; they are just all of the files in the Library that appeared to be related to GarageBand.