If you're a registered Apple developer, session 409 (in the Graphics and Media section) of this year's WWDC is a very good tutorial: http://developer.apple.com/videos/wwdc/2010/
here are more direct links ...
session 409:
http://adcdownload.apple.com//videos/wwdc_2010__sd/session_409__using_the_camera_with_av_foundation.mov
also, session 405 intro:
http://adcdownload.apple.com//videos/wwdc_2010__sd/session_405__discovering_av_foundation.mov
