A preprint from College & Research Libraries is well worth your read, even if you're not a webmaster: How Users Search the Library from a Single Search Box (from NCSU, Cory Lown, Tito Sierra, and Josh Boyer)
Academic libraries are turning increasingly to unified search solutions to simplify search and discovery of library resources. Unfortunately, very little research has been published on library user search behavior in single search box environments. This study examines how users search a large public university library using a prominent, single search box on the library website. The article examines two semesters of real-world data, totaling nearly 1.4 million transactions. Findings include that unified library search is about more than the catalog and articles, though these predominate. Additionally, a small number of the most popular search queries accounts for a disproportionate amount of the overall queries. Also discussed are the merits of ongoing evaluation of library user search behavior.
(it's not nearly as long as you'd think upon initial download; the last half of the PDF are the images and a couple of pages of references)