I've used Jive Clearspace/SBS for more than 3+ years (both internal and external), and I can honestly say it is one of the most extensible/agile pieces of Java-based technology I've used in my 12+ year industry career. It has been my experience that people who walk away from Jive with a negative experience tend to be 1 of 2 use-cases. 1.) Over customization of the product (as drivebyacct2 stated) or 2.) Those trying to make it something it is not, which is usually a Document Management system. In both these scenarios, Jive has made tremendous leaps forward in making extensions easier and more robust, while also partnering with platforms like Alfresco/Sharepoint for better Document Management capabilities. I strongly recommend those that haven't seen the product first-hand in the last 12 months, to check out the new Jive 5 Engage platform with What Matters. The difference maker (IMO) is that Jive has the best 6-12+ month user story when it comes to ramping up user collaboration and keeping them efficient in that collaboration as their social responsibilities grow in the face of exponentially louder activity streams and notification management complications. Those are my 2 cents.