We used Magnolia CMS for a prototype solution for a range of multilingual websites that are managed by their own department in that country. We investigated the product to create a solution for the client, who were looking for a content managed website solution.
I prefer Adobe CQ5 over Magnolia because I have more experience at using CQ5. I only gained a limited exposure to Magnolia on a prototyping exercise. I have used Adobe CQ5 for three years now. However, I would not object to learning Magnolia and giving a better comparison between the two content management systems.
I think that Magnolia CMS is a powerful tool, but I only had a limited experience of using it. I think it is probably costed effectively, but I prefer Adobe CQ5 CMS and find it easier to use and easier to set up. Magnolia CMS is very similar because it uses the JCR (technology).