Unless I'm missing something, their benchmark graphs at the bottom of the report show that there is no significant benefit to using SCM with MongoDB! Their internal overheads must be high enough to swamp the few microseconds gained from the faster storage.

That was my first thought, too. You need these tricks to make MongoDB "WebScale"

http://www.mongodb-is-web-scale.com/

(I can get better results for Key-Value storage by using an SQL Database--Postgres or MariaDB--for key/values over MongoDB. And if you know SQL well, you can get even better results using a real relational database and optimal queries than pulling out keys/values and ad-hocking your relations in some Javascript code or whatever these web kids are doing.)