If it's similar to the use case I'm in right now, we need a way to refresh the report using parameters that can only be set from outside of the ReportViewer...and we're using Silverlight MVVM.
The previous version allowed you to do this, and it worked quite well:
Now, as you mentioned, that breaks.
The issue with the work-around now is that my report does not have a child and the call to GetChild(ReportViewer, 0) now breaks with this error:
Specified argument was out of the range of valid values.
Parameter name: childIndex
I don't want to un-upgrade all the reports but that's what I'll have to do I guess...