Recently I received a request from a French musicologist for several of my mother's scores and recordings. Before IMSLP, the request would have plunged me into days of frenzied activity--making the recordings and the labels, copying and trimming the scores, then packaging everything super-carefully. Then I would race down to the post office, usually about 5 minutes before closing, fill out the customs forms and mail everything off, praying that nothing would break or bend on its several-thousand-mile journey.
NOW, however, I was able to simply tell my musicologist that everything she was seeking was available--for free--on IMSLP. Oh happy day--I love you IMSLP!