Where Is The "Summarize" Service On OS X Mavericks? In previous versions of OS X, you could find the Summarize service by highlighting the text you want to summarize, going to the app name menu, click service, and then clicking summarize.

Call me blind but I can't see this service on OS X Mavericks at all? It was really useful in previous versions of the OS so I really hope it hasn't been removed.
Turns out this feature has to be enabled now.
After I posted my screenshot I noticed the "Service Preferences..." menu item and clicked it.

Click that menu item, scroll down to where it says "Text" and tick the box that says "Summarize".