In trusty 14.04, the out-of-the-box install gives you a Unity file and folder search which provides relevance-based search for recently used files (through Zeitgeist) augmented with entire filesystem search (through mlocate).
However, as far as I can tell, there is no full-text search available for all documents on the filesystem. The existing Unity search lens does not do full-text search of document contents; rather, only the document names themselves. There was a lens called "recoll-lens" which leveraged Recoll to do a full text search which was packaged up through 12.04 Precise (as other answers mentioned back in 2011, here, here), but there is no official backport of recoll-lens packaged for 14.04.
Does anyone know of a repository which contains recoll-lens for 14.04, or if there are any other full-text search Unity lenses which work for 14.04?
(While I realize that 14.04 is not the last stable point release, it is the last stable LTS release as of the moment that I'm asking this question (10/2015), and the Ubuntu installs that I manage are on a LTS-only policy for stability).