Aaron and I are trying to get Jruby on Rails on DB2 to actually work. So far, we have been wrestling with the following issues:
We are driving our effort by porting existing projects that work with other databases, and seeing what breaks. We are not DB2 experts, so a lot of this is conjecture+test. We would love to join forces with anyone interested in getting the DB2 driver to first-class status. Give us a shout.