Facts: RM 97.73, rvm, ruby 1.9.2 and Rails 3, OS X, Oracle client (with ruby-oci8 2.0.4 and activerecord-oracle_enhanced-adapter 1.3.1), running the app from RM.
DB rails apps that use Oracle fail with the complaint that the activerecord-oracle_enhanced-adapter can't load ruby-oci8. ruby-oci8 connects ruby to the Oracle database client. I'm guessing RM doesn't inherit an execution environment that tells ruby-oci8 where to find the client and its configuration, hence it fails to load.
If I start RM from the command line, *does* have paths set in the proper way, the applications seems to run normally.
I've found this to be a common problem with OS X apps.