By the way, I also discovered that doing a cast in the DSV is unnecessary. Just right click on the measure, choose Properties, expand Source, then change the DataType appropriately. Most of my research on this subject got worked into the following BIDS Helper feature:

http://www.codeplex.com/bidshelper/Wiki/View.aspx?title=Measure%20Group%20Health%20Check

Also, in one cube I’ve worked on, we had to make this very decision in deciding whether to make the placeholder for assignments physical or calculated. It appeared that there was a 10% performance penalty if the measure was physical when the calc script is doing a bunch of leaf level assignments. (We theorized that the reason for this was that the calc script was aggregating after the assignments, but I can’t prove that.) In our case, we weren’t interested in those assignment aggregating, so there was no point in making the calculated measure physical. Just wanted to mention that it’s worth checking the performance of both alternatives.