The textbook Search Engines: Information Retrieval in Practice by Croft, Metzler and Strohman now has over 5,000 downloads. The book is available for free download at http://ciir.cs.umass.edu/irbook/. It has been edited to correct the minor errors noted in the 5 years since the book's publication. The authors, meanwhile, are working on a second edition. Posted: April 2016