This package is one of the many parts of the JasperSoft BI solution. I'm currently evaluating the JasperServer and below are my comments.
1. The documentation for JasperServer is terrible. Unlike other documentation which assumes that you don't know anything, JasperSoft assumes you know their stuff already. Because of this, it is quite hard to understand.
2. iReport which is the GUI interface to create JasperReport looks cool but I can't seem to get it working with JasperServer. Again, because of poor documentation or none at all. Oh wait! There is documentation which I think can be found in the 'JasperServer Ultimate Guide' which you have to buy for $50. Hmm, maybe a good way to make money for open source company. Create a nice looking open source software, but sell the documentation. Sweet!
3. I almost forgot this... when I was installing JasperServer, typically you would expect that if you have an error, the installation will stop or just let you know that there was a problem. With JasperServer, you have to look at the logs and make sure that you don't get any Java related errors. Sweet!
Well, I'm still evaluating this software but my other co-worker is evaluating InfoBright which I heard is a MySQL storage engine that compresses and makes your data ready for data warehouse processing.