I'd definitely be curious to see a comparison from someone who wrote an iPhone and iPad optimized version of an application and released in the same time frame.

The other thing I'd be interested in seeing is if someone did a study on the buying habits of iPad vs. iPhone (heck, lets generalize and say tablet vs. smartphone) application buyers. I have a feeling we'd see more apps being purchased in the smartphone arena as people buy-try-dump apps on the go, whereas there'd be a more stable market in the tablet space where people research which apps to buy because they use the tablet for longer durations.