Canon Professional Network (CPN) has posted three videos
describing the new Canon lenses.
The video describing the new Canon EF 300mm f/2.8L IS II USM Lens
and Canon EF 400mm f/2.8L IS II USM Lens
is the longest - going into the most depth. And I have to say, the weight reduction on the 400 is very dramatic - I can easily handhold this lens for periods of time.