Overclocking the lecture: consume recorded lectures much more quickly

First, for most lecturers it isn't possible to listen to recordings more than 1.5 times faster. At this rate, there is a roughly 33% reduction in the time it takes to view a lecture. It is noticeably faster, but not really significant unless you are viewing more than 1 lecture at a time, for example a lecture is typically 50 minutes, so one saves about 17 minutes per lecture. In my experience the savings fail to realize for the reasons I'll cover further.

Second, the rate at which the lecture can be accelerated varies significantly depending on the professor who is presenting the material. Some professors speak quickly and once the playback speed is increased to 1.5, their speech becomes blurred and unintelligible. Often the native English speakers are the ones who can't be sped up much. Luckily, at my school most of the professors aren't native speakers so a rate of 1.5 is adequate. For non-native speakers, the useful playback rate varies pretty widely. One of my professors who is from Turkey speaks slowly and his lectures can be played and understood at a speed up of 2.

Third, the playback speed does affect comprehension. Even at a normal playback rate I find that some topics covered in the lecture require a rewind and a replay. Accelerated playback requires closer attention and more frequent replays. Of course how often one needs to replay the lecture depends on the content and varies from person to person.