"Now that disk space is so cheap and many of the data models don't benefit as much from normalization, JOINs are easy to leave behind."

JOINs and data normalization were not created to get around disk space constraints.

http://en.wikipedia.org/wiki/Database_normalization#Objectiv...

For the average web application not running on app-engine like infrastructure, I believe the following order of questions would be more prudent:

   1. Do I need a database?
   2. Can I work with a relational database? SQLite? PostgreSQL/MySQL?
   3. Now, do I really need the new hotness?

And if you do need the new hotness, may I also suggest Tokyo Cabinet? I am afraid I can't rate its 'value' on a scale of 10, but I'd say it's pretty high for a free product.