The release of gmpc in Ubuntu 12.04 has support for unity (libappindicator) indicators, but unfortunately is currently built without it.
Merely adding libappindicator-dev to the build dependencies in debian/control is enough to make it work (I have tested it). Users who have already run the non-unity-supporting build will also need to change a hidden preference: in ~/.config/gmpc/gmpc.cfg, under the "tray-icon2" section, set use_appindicator to "1". A note to this effect could usefully be put in README.Debian.
It would be a great pity not to have appindicator support for Ubuntu's default desktop (unity) in Precise, so could this possibly be done in time for beta 2?
ProblemType: Bug
DistroRelease: Ubuntu 12.04
Package: gmpc 11.8.16-2
ProcVersionSignature: Ubuntu 3.2.0-18.29-generic 3.2.9
Uname: Linux 3.2.0-18-generic x86_64
ApportVersion: 1.94.1-0ubuntu2
Architecture: amd64
Date: Thu Mar 15 21:33:01 2012
InstallationMedia: Ubuntu 11.04 "Natty Narwhal" - Release amd64 (20110427.1)
SourcePackage: gmpc
UpgradeStatus: Upgraded to precise on 2012-03-06 (9 days ago)
Status changed to 'Confirmed' because the bug affects multiple users.