I think that many of the NoSQL crowd either fail to either recognize, or to properly describe that their preferred databases don’t replace applications like MySQL and Postgres, just as Ruby doesn’t replace Java. Instead, the explosion of these new options for persistence just work better for some domains (and worse for others).
Ben Scofield’s spot-on here. One of the many transitions we’re undergoing is from “I’ll use MySQL most of my career” to “I’ll tinker with a different database for every project over a couple years and then pick and choose the best as time goes on”.