Here's the chart:
http://www.aanegotiations.com/documents/AAFACharts_7.8.10.pdf
For the 12 months ended 5/2010 (6/09 - 5/10), 3,621 FAs, or 22.6% of active FAs, flew less than 40 hours per month on average. 577 flew no hours at all. 1,300 flew less than 20 hours per month on average.
The chart doesn't tell us how many drop every trip every month, but it does show a lot of part-time FAs.
AA has said that the scheduling limits are the real problem. If AA were allowed to schedule FAs for 15-20 more hours per month, AA would need fewer FAs (leading to cost savings). FAs could still drop their trips as they do now, but of course there would be fewer FAs to pick them up. Could be that some FAs who don't fly now would have to fly a trip or two if they had trips with no takers.
I'll find my own 15-20 hrs to PU, let us chose our own crap, since the lines and trips are ugly anyway.