I have both Fedora 16 and openSUSE 12.1. In both systems I have the same problem with Audacity 2.0. When I go to Edit > Preferences and hit ok the top menu disappears. Only Fil is displayed as shown here http://wstaw.org/m/2012/05/13/Audacity.png.
It’s a known bug related to the version of WxWidgets. It seems to occur when Audacity is built against WxWidgets 2.8.12.
If you look in Audacity “Help > About Audacity > Build Information” it should say, in the “core libraries” section, which version of WxWidgets Audacity was built with.
The workaround (I’ve only tested this on Debian based distros) is to resize the window and the menus should then reappear.
In openSUSE I installed it from the official repository whereas in Fedora 16 I think I installed it from rpmfusion. I may have buit it from source as Fedora’s version doesn’t support mp3. Nevertheless, they both behave identically regarding this bug.
The bug was already listed on the Audacity bug tracker, but as it did not occur with any “official” builds it was allocated a fairly low status. Now that distros are updating their version of WxWidgets the bug is starting to appear in those official builds and the situation will only get worse 'till it is fixed, so the priority has now been raised so now it is listed as very high priority (“P2”).
Just for the record this problem exist in Ubuntu Studio 12.04 when running with Xfce desktop. The problem does not exist in Ubuntu 12.04 with Unity desktop. In Unity the menu is in the top panel and not in the app’s window.