It's also interesting to look at the labels on our food in the US. Spaghetti sauce? Added sugar. Loaf of whole wheat bread? Added sugar. People may not see the addiction, but it's added to most everything right in front of our face.
I have a few quick thoughts about why you're not getting many sign-ups.
The copy on the landing page makes sense, but it's still confusing in a way. Maybe if you had a small diagram or brief description on how this is done, people might be more interested.
But, if I was interested I would be weary of oauthing on twitter because I'm still not sure what or how you do what you claim to.
The video should probably be less than 60 seconds and should answer what the service does, how, why, for who in the first 20 seconds.
Stumbleupon traffic doesn't work well. People are simply browsing from one site to the next looking for articles or funny cats and your bounce rate using SU is probably 100%.