Is there anyone out there that used these two technologies and could give me some comparison in the form of advantages and disadvantages of both? I'm currently working with BO and I have heard that open source Pentaho does pretty good job as well. Thanks in advance!
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.