Alberto Ferrari posted an interesting article that show how you can use a continuous value in a group of values in PowerPivot. I think this is a feature that many users would like to get in a standard Analysis Services cube, but that unfortunately requires to change the cube structure on the server, something that an end user is not allowed to do.
Having such a flexibility in PowerPivot is one of the reasons it should be adopted by data analysts and advanced Excel users to do advanced analysis in a more autonomous way. The same topic is covered in more details in the Microsoft® PowerPivot for Excel® 2010: Give Your Data Meaning book (which is finally in stock – I just received my hard copy a few days ago and I’m happy it is now on my shelf, too) and will be of course discussed in the PowerPivot Workshop on Dec. 1-2, 2010.