Maciej reported in his blog that Magnolia CMS uses jBPM 5 as their default work flow engine in version 5.
Just two weeks ago I had a pleasure to talk about jBPM (both v5 and v6) at Magnolia conference in Basel, Switzerland. This was a great event that I recommend everyone that is interested in CMS.
Together with Espen from Magnolia team, we made a really nice presentation about both jBPM and Magnolia Workflow that utilizes jBPM.
Here you can find the presentation: