I belong the the STN/Student Television Network listserve and got this comment from John King of the Metropolitan School District of Washington Township, Indianapolis:

To make the most of hard drive cameras you need to offload the material as soon as possible because a full hard drive means a useless camera. Even if you take a laptop to the field, time and battery is spent transferring video. Reloading tapes means the camera can stay out all day long.

Excellent points – the consumer hard drive cameras have the hard drive built in. Once it is full, you are out of space. Pro cameras have removable (very expensive) modules.
My other concern w/hard drive camcorders (as a teacher) is the problem determining who shot which clips when you finally go to download…when multiple students share a camera.