Here's the classic slo mo strobe video:
http://techtv.mit.edu/file/146/
(full screen recommended)

But check it after reading the 2005 press release about "discovering" 75% lift from down (forward ) stroke, and the rest from upstroke.   
http://www.nsf.gov/news/news_summ.jsp?cntn_id=104263

(Resting pulse 40 - flying 500 bpm.)