Here is a fantastic post by our friends at See3:
We would just like to add that Sparks are IAB compliant and can be distributed through ad networks like DoubleClick. Here is what Evan Moody from Blue State Digital had to say about using Sparks as rich media ad units:
“We loved using Sparks for our media buy. The value add is that these widgets give supporters the ability to sign the petition, tweet, and share more readily and the fact that we didn't have to pay per impression served is great.”