If anyone was wondering... here's a link to an article that talks about that. It's interesting that Microsoft had a hand in the research.
I read yesterday that Ad supported Apps use up to 60% more battery due to poorly written ad engines.
Angry Birds was one of the apps they tested.
While playing a level of Angry Birds, 70 percent of the battery drain was as a result of the game uploading user data in the background, such as location information) and the downloading and displaying of ads to the user.