Today I was surprised. Looking for some references I have found on the Microsoft website that not only DBPL, ISI, etc. but also the Microsoft Academic Search is indexing the different research papers, counting the references, counting the number of citations and the co-authors of my papers. G-index, H-index is also calculated.
Even more, you can have citation-graphs, co-author graphs and co-author paths. And the surprise was: my Erdos number has been reduced from 5 to 4. It means that I have a co-author who's Erdos number is 3. The Erdos number of Paul Erdos is 0. As you might have realized, this is a recursive definition of the Erdos function (Erdos number).