Well, I suppose it would be possible to implement a revenue share per download system, but personally I think you'd be better off placing most of the burden for increased security on the Admin end (and those that volunteer) than you would be on the user end.
Take myself for example.. pretty much average joe blow internet guy. I'm out bouncing around another board when I come across some freebies offered on another website.
First few I click all take me here to sharecg - a site I'd never heard of before and one that I had no knowledge of whatsoever. So I get curious, start poking around and viola! Feel like I hit the jackpot as far as 3d freebies are concerned.
Now.. lets back that up a bit and say that I get here to sharecg and it asks me to register before I download anything. This is getting much more common out there and believe me, from a user perspective it's getting to be a huge pain in the keester.
Alright, sure, if I'm leaving messages on a message base or becoming part of the community I can see you asking me for some personal information, that's all well and good. But hell I didn't come here to fill out a bunch of damn forms, I just wanted one freebie and now I feel irritated. Another site that's wanting me to fill out paperwork and give out information I don't like giving out, and yes my email address is something I don't like giving out till I've had a chance to get to see the site and see if it's worth giving my email address too.
I'm went through several yahoo email addresses this last year, I use them to keep my actual email address safe. I've had to close mulitple yahoo accounts because I do a lot on the web, and after giving those addresses out to only a handful of sites they get spammed to death. I had one account that was averaging almost 10 megs worth of email a day, and all I wanted from the site in question was a simple tutorial.
Point being, if sharecg had asked me to login and register for that first download, I'm not entirely certain I would have done it. Granted, looking back now that I know a bit about sharecg I would consider it a no brainer, I'd sign up in a heartbeat. But the very first time I ended up at sharecg by following a download link, I had no idea what sharecg was or what it had to offer. I was just a guy looking for a prop file for a particular scene and I didn't want to take the time to create it myself.
Granted, ultimately this is someone elses site and they must decide how best to protect it from scammers. But this thread was started to ask for suggestions and that's just what I did, gave them what I considered to be the best solution to the problem.