Every choice you make in software has pros/cons. This is true of all database technologies as well. You can probably solve your problem using any of the choices before you. If you decide to use something new (e.g. MongoDB, Riak, whatever) first make sure it lines up with your requirements then see how it goes. Always keep backups. In the worst case, you'll restore and migrate to something else. But that's kind of what we do as an industry anyways.