Like you I have seen a demo of PowerPivot and was impressed by what it can do, but I find it a little scary. Its very easy to design a bad data warehouse and because of the design incorrect figures get churned out as a result, how much easier is it now going to be to produce bad results.

I hope that common sense rules when rolling this product out, but I've been in IT to long and doubt that will happen, I can see moderately capable users using this product believing that they are now Data Warehouse specialist and lots of bad statistics resulting.