There are some changes happening, but certainly MySQL will dominate pre-existing installs for the foreseeable future. Switching databases is not trivial for most applications.

Here's a blog post from 451Group in May 2012 about a survey they did: http://blogs.the451group.com/information_management/2012/05/...

And a specific bit of the presentation linked from there that I found interesting: http://www.slideshare.net/mattaslett/mysql-vs-nosql-and-news...

Slide 20.

It's certainly not conclusive, but it is interesting.