I tried it on my proxy list site for an hour or so, I quickly removed.
I know someone who is having a little success running on regular proxies.
I believe he lets them browse quite a few pages then asks them to complete a survey - they have the choice at this stage to refuse and carry on browsing.
After another batch of pages again they are asked and then after a while you are forced to complete one.
No shame refferral link: http://www.cpalead.com/apply.php?ref=20104
I do recommend people check them out for other projects