"I switched to TC to begin with because I was using SQL wrong, and it was too slow and clumsy. Once I figured out how to use SQL correctly, it was a no-brainer to go back."

While k-v stores and other NoSQL solutions have many great, valid use-cases, I expect there are many other people who switched to NoSQL stores on the basis that they were "faster" only to discover that they needed many of the features they'd left behind in SQL databases.