Freebase makes their data available as free CC-licensed data dumps. You can import this into any database you want. There's no requirement for Metaweb's technology to use the data. It's just a very convenient way to do so!
Early on, we knew we'd have to make a UI so that users could have as close to a free-text experience as possible while still contributing structured data. Freebase lets you create a topic that is generic, and then co-type it with multiple specific types later. It allows ontology geeks to do their thing, and regular users to just work where they are comfortable. It's a tough balance to strike, but Metaweb's Freebase was populated by a small team of data wranglers using a mix of automated methods and coordinated manual cleanup and entry, along with power users who were especially interested in particular data domains.
At one point I was really interested in submarines. I created a type describing the key characterists of subs and then spent a few days finding all the generic topics in Freebase on subs (many from Wikipedia) and filling them in. Others, either at Metaweb or outside, have done similar efforts on other domains.
Few contributors ever say or even have to consider ontologies. If they want to dig in, it's there, but almost never presented in a way that requires a PhD and a pipe.
This is a good point. I don't know if this was a factor in Google's acquisition, but Powerset (acquired by Microsoft and now part of Bing) uses Metaweb's Freebase.
I was on the founding team at Metaweb when we spun out of Applied Minds. I can answer some questions here, but first I wanted to congratulate the team that brought this company all the way to acquisition.
So, from the beginning we knew that semantic this and ontology that would be a non-starter for most contributors from Planet Earth. While Freebase is a complex system under the hood, the user interface makes contributing data to an existing type (schema) pretty easy. You can add content from a browser window and never know that all of your entries are typed by the system. You can upload a spreadsheet of data and not have to do anything more than say which column is linked to what field in Freebase.
My startup, 24 Hr. Diner, uses Freebase to demo our artist to artist recommendation engine, Jukebox. We have recommendations for 100k artists, and for each of them, we can look up their genre info and photo on Freebase without having to maintain all of that data ourselves.
And if anyone on Slashdot is working for a co. that could use an excellent recommendation engine that handles music, videos, and general web content, ping me!
MATH AND ALCOHOL DON'T MIX! Please, don't drink and derive. Mathematicians Against Drunk Deriving