One of the annoying aspects of OS X are all the half-baked ideas. I guess it's a problem with having a creative design team that's more interested in invention then implementation. OS X Services is in this class; promising but undeveloped. Some applications support them, many don't. They don't work with Firefox, but in Safari you can highlight text and apply several services to the text. AppleWorks doesn't support Services, but TextEdit and OmniOutliner do.
Random Tech has a good article on how to get the most from services, including a link to some DevonThink freeware I'm going to try out: Random Tech: Mac OS X Services (the menu you never go to).
Update: I'm impressed with the great DevonTech gifts. This may push me from Firefox back to Safari!