Hi folks,
this is actually not a question but an announcement: due to the fact that gmusicbrowser will be shipped in Xubuntu Natty by default and my involvement there I decided to switch the supported panels from
* xfce<=4.6, lxpanel, fluxbox

to
* xfce>=4.7, gnome-panel

This means that currently in all panels from the first list (and maybe others that I haven't tested personally) the trayicon will not have a transparent background. I have discussed this issue with Quentin and in the long run there will (most likely) be a switch in the trayicon-preferences (which will at that point most likely be a separate plugin) for the user to easily decide which panels to support.
Unfortunately it's practically impossible to determine what panel is in use or whether the panel supports real alpha-transparency (which is - in my understanding - the reason for this issue).

Users of Xubuntu Maverick will experience a non-transparent background in their systray-icon, I apologize for the inconvenience. If you want to fix the problem yourself edit the file "/usr/bin/gmusicbrowser" (you'll need superuser rights for that) and comment this line by adding a leading "#":
Layout::Window::make_transparent($TrayIcon) if $CairoOK;