FYI: Remember the "Vienna phonebook thread"? The archival collection we used to find all that information is (finally) being opened to the public with a presentation tomorrow afternoon here at the Holocaust Museum in Washington.
I'm back from Vienna, where--thanks to the answers that came from this AskMe thread--I was able to visit the building where my mom lived as a little girl, as well as the location where my grandparents' grocery store likely once stood. I've posted some photos in the thread, for anybody who is interested. Thanks again to arco and his colleague at the USHMM.