Mixed feelings about this... completely agree that free downloaders only use valuable resources, and they should be 'pushed' a bit to buy premium. Also agree that free users should generate some money too.
But I feel that some advertisement program would be better as installing software on their systems, especially as it seems that many anti virus programs report it as a virus/trojan. (btw, I tried it on my linux system, it's just not working :p ) Pissing of people by installing (possible) virus infected software on their PC doesn't look like the perfect sales argument to me ;-(
I'm not a big fan of fiberupload, but it looks to me that they found a nice mix between advertisement/functionality. Think you should have a look at it.
But if you decide to go on with it, please note clearly on the site that premium users don't have to solve captcha's, now it looks like everyone has to do ...
And for the guy with the statistics, no, I will not run away if it's implemented. If my users are unhappy with it, that's their problem. If sales drop, that's FM's problem, but in that case he will probably stop the program. If it works, everyone will be happy as FM promised us some time ago a PPD program for these downloads. If I want real big money, I will have to work for it, this is just a hobby ;-)