if you're using them, have you earned much? about the same as your other adsense units? is it worth it? the last time i checked, it's a mix of cost per click and cost per impression. is this still the case? i would think it would only be worth it if they were cost per impression. also, maybe i didn't toy around with it a lot, but, is there any way that you can have the ads appear on just youtube videos that you select?