If you have 30 seconds available, please vote the following items on Connect:
When you import data coming from an Analysis Services cube in PowerPivot, you cannot import the attribute key value. Only the attribute name is included in the query generated by the query designer. There is a possible workaround, creating a calculated measure with an MDX expression which return the attribute key value corresponding to the current member of the related attribute, but not many users are able to do that.
When you import data coming from an Analysis Services cube in PowerPivot, you cannot import a ragged hierarchy. I've already described this issue in an older post.
The reason I ask your support is that in Denali CTP3 both PowerPivot and BIDS for Tabular projects has these issues. It really hurts PowerPivot end users, but it is also a waste of time for the experienced BI developer, who need to write a calculated measure in MDX for each attribute key he wants to import it using the query designer (writing MDX by hand is always the preferred alternative, I know) and have to write an MDX query by hand if the levels in the ragged hierarchy are not exposed as browsable attributes (which is not a best practice in cube design!).
Help me to rais the priority for this issues - A multidimensional model in Analysis Services should be a better data source for PowerPivot and BISM Tabular!