ACKNOWLEDGEMENTS Many people helped make this dissertation a reality. First, I would like to thank my hesis committee, John Riedl, John Carlis, Paul Garrett, and Joseph Konstan. I would especially like to thank Joe for being a fantastic advisor; I have learned more from you than you realize. Thank you to my paper writing colleagues, especially Roberto Torres, Jr and Cai-Nicholas Ziegler, it was wonderful working with you. Thank you to everyone in GroupLens Research, especially Dan Cosley, Al Mamunur(Mamun) Rashid, and Shyong(Tony) Lam. Because of your support, encouragement, and friendship, GroupLens Research is a special place. Thanks also those who've already gotten their Ph. D. from Minnesota for their support and encouragement, including Jon Herlocker, Brad Miller, J. Ben Schafer, Brian Bailey, Harini Veeraraghavan, and Doug Perrin. I would also like to thank Ed H Chi for his support and advice during my graduate school career. I have been blessed with many great teachers and professors, especially Jack Goldfeather and Jeff Ondich from Carleton College who showed me the love of computer science, and my sophomore year high school English teacher, Mrs. Skoy. As far as I know, I still have extra credit"in her heart". Finally, I want to thank my wonderful group of friends, my family, and everyone who helped and supported me through this process. I could not have done it otherwise. In a different set of thanks, i want to thank the University of Minnesota Computer Science department Systems Staff for keeping all of the machines running. Thanks also to nec Research for the ResearchIndex data, thanks to Book Crossing. com for allowing us to collect data and run experiments, and thanks to the ACM for providing us with data from the ACM Digital Library Reproduced with permission of the copyright owner. Further reproduction prohibited without permissionReproduced with permission of the copyright owner. Further reproduction prohibited without permission