First of all, great video by JL-Dub. I am subscribing to your Youtube channel and we might have to talk - I got some pretty high level ideas I would like to bounce by someone like you...
2nd - I am assuming we are talking about stumbleupon paid discovery. I have been using this for about a year. I have tried many different things and there are two ways to bank, only one I have been able to use long term.
1. The first method was with a panic attack site, for panic-away on click bank. I was writing stories about celebrities who had panic attacks and paying for stumbles. I was actually getting people to sign up for my free 6 day panic email series with a panic away sell at the end. Also I was running adsense and those clicks were like $1.25 per - mostly anxiety med ads. I would spend $100 and make $130. It was money. Then stumbleupon stopped rejecting those articles and then my site all together. I tried a few more things around that (stuttering, etc) creating entire sites and never getting back on stumble.
2. The second way I still use. This is for sites that post frequently. I have a Movie site, gossip site, weird news site, and a funny bullsh*t type of site. These are updated everyday, multiple times per day. When you pay for stumbles, it gets you into the stumbleupon system and you start to get traffic from them. Sometime it takes just like a $10 spend and a good story or it takes a month of spending like $20 per week.
The key is, you have to then stumble your posts after that. I really can't tell you how it works, but it does.
Before I used paid discovery I would stumble each post and it would sit at only 1 stumble. Now I get 1000's per day for a stretch. When I notice I'm not getting them anymore, I prime the pump with another $10, check...if still, another $10...and usually by about $50 max, I'm getting regular stumbles again. As you can see from the pic the traffic is adsense safe, and you do get clicks but not alot. I would have to look at the CTR but it does pay for itself. Plus your Alex number drops, your Page Rank increases and all the other benefits of getting real people traffic.
That's the only way I have been able to consistently use Stumbleupon PPC
Good Luck
-Capp