Title says it all. If you install tracker, deskbar-applet crashes at startup. I don't know if it's an upstream bug or fc7 specific. I let bug-buddy file an upstream bug here: http://bugzilla.gnome.org/show_bug.cgi?id=426225 deskbar-applet-2.18.0-1.fc7.i386, tracker-0.5.4-6.fc7.i386
I pushed out deskbar-applet-2.18.1 for FC7, please see if that resolves your problem. Also, tracker isn't officially supported by deskbar-applet yet, so there isn't much we can do about this issue at the moment.