Here is some good news from sharepoint designer team
Just surfed on this topic SPDataSource and Rollups with the Data View
And i think it answers many of the questions on the forum on how to have a view of multiple lists cross sites and subsites etc..Although i have managed to do the same using some other workarounds i would alo find time to try this solution too.
There are also some couple of other workarounds and also a webpart i found very useful
I would be blogging on them very soon.
Cya