Because xdg-screensaver doesn't use Gnome 3's D-Bus API, screensaver enabling/disabling does not work. There already is an upstream patch for this: http://cgit.freedesktop.org/xdg/xdg-utils/commit/?id=666d65cae0f2e66d33ec0dc48c054afbf16c9e3f
xdg-utils-1.1.0-0.9.20110714.fc16 is an upstream snapshot from 2011-07-14 far beyond when that aforementioned upstream commit occurred 2011-03-31 so, is xdg-screensaver not working for you for some other reason perhaps?
In the meantime, please try, https://admin.fedoraproject.org/updates/FEDORA-2011-16850/xdg-utils-1.1.0-0.10.20111207.fc16
xdg-utils-1.1.0-0.10.20111207.fc16 has been submitted as an update for Fedora 16. https://admin.fedoraproject.org/updates/FEDORA-2011-16850/xdg-utils-1.1.0-0.10.20111207.fc16
xdg-utils-1.1.0-0.10.20111207.fc16 has been pushed to the Fedora 16 stable repository. If problems still persist, please make note of it in this bug report.