Another observation that struck me when I read this (and after reading the percolator and megastore papers) is how there is a convergence of the "traditional" relational DB world and the "new NoSQL" world. Relational Databases are becoming more scalable, partially with new technology, partially by shedding features in some scenarios. And the NoSQL stores, are becoming less so (it was really about "NoSQL" anyway, but that's a different story). All of these stores have layers or features that bring closer to the traditional SQL/relational model.

Spanner appears to strike a nice middle ground.