Smart Scopes were supposed to be an intelligent server-side service for deciding if a search query should be pushed through a particular scope, among other benefits. Smart scopes were said to be self-learning and aimed to provide more relevant results for users of the Unity desktop.
Jono Bacon has now shared via his blog that "smart scopes" are not ready to ship in Ubuntu 13.04 but will be postponed to Ubuntu 13.10. Mark Shuttleworth ultimately decided the feature wasn't ready for Ubuntu 13.04 "Raring Ringtail" and had to be postponed.
More details can be found on Jono Bacon's blog.