I haven't used Über, but the idea is exactly the same and the apps are very much alike. I live in Madrid, which is one of the cities where Cabify operates. I've used their service a couple of times and I can only recommend it. Looks like a good place to work and Mark Villa Camp, the guy mentioned in the article is a well known name in the Spanish tech scene.

Is Cabify a copycat? Whatever, is a well executed idea and I wish they succeed.