I've just read about a university here in Sweden that has banned students from filming lectures and publishing them on the net without the teacher's permission.
This is a delicate question and shows that education is facing the problems already well known in the music and film industry. Since everyone in class owns a mobile terminal with built-in film camera it's not surprising that students are recording lectures so that they can listen to later. Copyright questions abound here just as in the case of recording a concert or any other live event. Sometimes there is a legitimate reason for recording a lecture, especially for people with impaired hearing or difficulties in taking notes, and a quick word with the teacher beforehand will normally result in permission to record. However it's not acceptable for a teacher to hear later that her/his latest seminar is already out on YouTube.
Maybe we need to discuss with students on a code of practice for this sort of thing and agree on certain groundrules. Most will abide by these. Those who don't are very hard to tackle and there will always be people who get a kick out of breaking any rules no matter how reasonable.
Another point is why they want to record classes. It's actually positive that they want a record of your classes for future reference. Maybe if all classes were recorded and available on the net afterwards there would be little point in recording them on a cellphone. Once again the example of iTunes U points the way.
On the other hand if all lectures are filmed and put out on the net why bother to turn up at all? If it's one way communication then it may as well be on the net. But learning is about participation and interaction and that's where the live event cannot be replaced by a recording.
This debate will run and run and there's no simple solution. However, we can be certain that mobile devices will only become even more powerful and easier to use and that they are here to stay. We have to adapt, just as many other parts of society are doing.