Xeround looks really interesting (http://xeround.com/).
Seems to do everything in RAM and takes care of any replication / backup & scailing for you. Looks like it would get expensive with large amounts of data though... anyone using this in production?
One of the things that separate us from Xeround is the fact that you can see the benefit of super high throughput on any linux box, including your laptop. You can download the software and use it by yourself.
Xeround is a sas model, where you can't get exact same experience as on your local machine.
Ycombinator seems to have backed a few of these next-gen databases. It will be interesting to see who wins.
EDIT: Rethinkdb. But it looks liked they've dumped their mysql engine and gone to a pure key-value store.