Pentaho is a full-fledged BI suite, meaning it can handle everything from reports, OLAP, dashboards, etc.
I ve only briefly dealt with the reporting side of BO, but I haven t looked to any other systems since starting to work with Pentaho three years ago. It s a very powerful system (and FOSS). There s also a very vibrant and active community. Being FOSS, Pentaho also encourages the community to contribute back. Some recent examples of this are Saiku (previously called Pentaho Analysis Tool; 1.0 is around the corner, already usable as a plugin into the BI server) and the Community Dashboard Framework (which is now a core component of the suite).
The best suggestion I can make is to download the test server from Sourceforge and start playing with the toolset. It s free, so there s no trial expiration to worry about.
Pentaho also provides support packages for both individual components and the full suite. The last time I checked the prices, it was like $2.5k for a component and $10k for up to 10 developers on a single server.