I just released mondrian-olap gem version 0.3.0. The big change is that it now includes latest snapshot of Mondrian 3.3.0 version (see Mondrian version announcement at
http://mondrian.pentaho.com/).
I upgraded and tested also sample mondrian_demo Rails application to latest mondrian-olap version and Rails 3.1.1 and all examples are running fine.
The largest application that uses mondrian-olap probably is my eazyBI application (
https://eazybi.com). I have upgraded it as well to latest mondrian-olap version and Mondrian 3.3.0 and all reports are running fine so I think it is safe for everyone to migrate to this new version :)
If you still find any bugs either in mondrian-olap or in Mondrian 3.3.0 then please report them (there was one Mondrian bug which I found during eazyBI upgrade but one of Mondrian key developers was very fast and fixed it in couple hours).
Raimonds