tracker-search-tool-0.5.4-2.fc6 installs tracker-handler.py* to /usr/lib/python2.4/site-packages/deskbar/ but deskbar-applet looks for handlers in /usr/lib/deskbar-applet/handlers. The result is that deskbar does not offer the option to enable tracker support in its preferences. Tracker's configure can automatically detect the correct location via pkg-config if deskbar-applet & pkgconfig are added as BuildRequires or "configure --with-deskbar-applet-handler-dir" can be used to set it manually.
Thanks for the bug report. Having both deskbar-applet and pkgconfig as BuildRequires doesn't make tracker automatically configure the right location in released ver-0.5.4 (i believe it does with the with the upstream svn). In any case, the bug is resolved by installing the deskbar plugin in the right place.