We had a second great discussion with Lee Graber and Venky Veeraraghavan and our MS Account Team today.  They are actively working on getting a solution to allow PowerPivot to work with Windows Claims Authentication in SharePoint 2010, as I talked about in my previous post.  They are expecting to down select an approach, from 4 down to 1, by the end of the week and give us an update on what the timeline will look like.This has been a great experience working with the two product teams, SharePoint and PowerPivot.  Everyone at Microsoft is very dedicated to getting a solution that will not only work for this one customer (us), but for the general population as well.I will update again once I have more to report!