Spotlight, as in the underlying search technology and APIs originating from Mac OS X 10.4, is fantastic. Spotlight, as in the search box that appears when hitting Cmd+Space has become obnoxious and commonly thinks I want to know what 1 pascal is in inHg when I type "1pa" instead of thinking I want to open 1Password.

To this day Alfred remains one of the first things I install on a new Mac as a result. Still have access to Spotlight (the indexing service) search, but none of the extra "intelligence" (aka Spotlight the app thinking it knows better than me what I want) unless I explicitly ask for it by explicitly invoking an extra workflow for things like unit conversion, etc.