Our class runs our own recording group which is responsible for hooking up the mp3 recorder to the mic system and then uploading lectures online. Most of the top students in our class never go to lecture, but use the mp3s + powerpoints instead.
Personally, I use Windows Media Player and listen on 2x speed. WMP does not increase pitch when speed is increased, so lecturers simply sound excited about their topic rather than sounding like chipmunks.
Advantages: I pause when I need to add notes to the powerpoints, rewind when I missed a point, and usually end up finishing lectures in 75% of the time.
Disadvantages: I got used to listening to people talk really fast, and now, being required to attend lectures in 3rd year, I'm dieing of boredom because people speak so "slowly."