There is an interesting paper in this week's Science magazine that suggests that being tested might be an essential component of making what we study part of longterm memory.  In the study, students had memorize Swahili-English word pairs.  According to the authors, "Repeated studying after learning had no effect on delayed recall, but repeated testing produced a large positive effect."

" The Critical Importance of Retrieval for Learning," by Jeffrey D. Karpicke and Henry L. Roediger, III2, Science 15 February 2008: Vol. 319. no. 5865, pp. 966 - 968