Mono Oracle client (System.Data.OracleClient) requires OCI binaries to work. Thus I suggest adding an 'oracle' USE flag to the dev-lang/mono ebuild, which would pull in dev-db/oracle-instantclient-basic as a dependency (for libclntsh.so).
+ 29 Jan 2009; Peter Alfredsen <loki_val@gentoo.org> mono-2.2-r3.ebuild: + Add postinst message pointing to the additional packages that must be + installed to support all mono namespaces w.r.t. bug 151315 and bug 256506. + Further investigation has revealed that the gluezilla package is not a + build-time dependency. The same is true for the Oracle instantclient. The + mono dlls for these will be built regardless, one only has to install the + packages to get support for them. + I'm sorry, but we can't add a useflag. The mono dlls are built regardless, so if one changed useflags and performed emerge -uDNav world, mono would be rebuilt with no good reason.