In the last year, many people begin talking about the open source software for BI. In fact, if you see the trends in source forge you'll see a huge increase in the downloads from this site.
But the question is not about “traditional BI” vs. “open source BI”, to me the question is about the maturity of the open source solutions.
We're clear that if we buy a traditional BI solution, we're buying software from a company with a reputation, several projects developed in different markets and the two most important things, a clear roadmap of the platform and an support service free for the first year and for subscription for the next years.
In the last two year, many BI companies were sold. Oracle bought Siebel and Hyperion (and many other little companies), SAP bought Business Objects, IBM bought Cognos and so on.
In most of the cases, the company who buy say that the want to continue with the development of the products they've bought, but nobody really know if it will be true. In fact Oracle is going to integrate Siebel and Hyperion to their suite.
But now, going to the open source BI, the big question is about the maturity of the software and on the other hand if the companies can survive only with the software subscription programs.
When a company make the decision to select a open source BI, must have in mind that if is true that open source means “for free”, they've to invest in a good consulting firm to drive the project in order to assure the success of the implementation. Also, is good to know the success stories of the software house, if they have certified partners in your country, the product roadmap and if the software house was consistent in their growing.
Most of the open source BI companies have a complete suite going for operational reporting to dashboards and from data mining features to ETL tools. However, you've to be careful because some times some solutions are not strong and you can experience some issues (data mining tools is an example).
Another important point, is the software subscription. If is so that open source means that anybody can modify the code to have the right solution for your company, its highly recommended to take the software subscription and let the software house to deliver the right version and use the internal consultants to maintain the application.
Most of the open source BI software are made in Java, that is very easy to modify and configure in order to obtain the right product for your company, but always talking to modify the products features but not the product kernel.