Yes, used many times - it's a half decent nosql document oriented store, however if you don't know the difference between an SQL based RDBMS and a document oriented stores like Mongo/Couch, then I'd suggest you do some reading first. If you do know the difference and are prepared to dive in, then Mongo or CouchDB are a good starting point. I'd advise using on a test / dummy project for your first time though, until you get used to what it's all about. see also: http://nosql-database.org/ & http://architects.dzone.com/articles/what-nosql-store-should-i-use
I used it for a project at work, but it did not scale well. It became bloated quickly and pages took 2+ minutes to load (for 50,000 records). Spent several weeks redoing everything in a relational database and now it's down to fractions of a second response time.