I've seen quite a few demos (esp. involving Power View) where the visualization being demonstrated looks fantastic, but it actually doesn't say anything useful (or takes up a lot of space to say very little).

When it comes to reports & visualizations, the most basic question I ask is "What action will you take based on this report?". Often people have very fixed ideas of what they want to see, and this question gets past that and helps me ensure that the final result meets that goal.