My style of leaving feedback is just to reference my ipod every so often to see which ones I had listened to recently out of the batch I have on there (I am also one of those who downloads several stories at once). Then I just look 'em up in the audiofic archive, click the comment to reader link, and leave a comment. I don't comment on everything I listen to (though I am trying to do better at that), but I can usually remember enough of what I thought of the podfic I'd listened to recently to leave a relevant comment. Then I take those stories off my ipod and add some new ones!