Sometimes Services in Snow Leopard stop working for no apparent reason. The menu is missing from the contextual menu items when you do a right-click, and the Services menu in the menu bar shows only 'Building...' Other times, there may be more than one entry for the same service. These problems can always (in my experience) be corrected without logging out or rebooting.
The technique is simple. Run the following command in a Terminal window or Automator workflow:
/System/Library/CoreServices/pbs
That's all there is to it. Your Services should now be working.
[crarko adds: A more little explanation is good for this one; the pbs utility is a debugging tool (follow the link, and scroll down to 'Testing' at the bottom) related to the Pasteboard Service in Cocoa. Running it will force a rescan of Services which is why the above will work. It's been mentioned in a previous hint back in 2004, so it's been around for a while. I doubt anyone noticed if there was a problem with Services prior to 10.6. Apple mentions that it could change or be removed at some point, so don't depend on it indefinitely.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20100805100621261