My torts prof would only give you his Powerpoint file if you had been absent that day if you agreed to delete the file within the week or whatever. It makes a lot of sense; a lot of them are working on books or articles, and ideas from those make it to class, so the profs really want to guard their shiny new ideas. AND if they get out ahead of time, and/or they're misapprehended, the prof loses a lot of control over the idea and its packaging. So, yeah. Don't record lectures without asking first. Like, ever. Although I do disagree with Moni about the value of what your prof is saying. Some profs, sure--nothing they say in class is ever relevant. But I had a number of classes this year where key stuff from class was on/constituted a major portion of/was relevant to the final. Including one class with a professor whose final the previous semester had had nothing to do with class discussion. I think it depends.