We have a very nice Java-Application at our side, and wanted to speed up the performance with the OracleDataSource (before we were working with Standard JDBC).
So we tested a lot and the performance was slightly better in the test-environment than before.After that we went to production with it.... and the phones began to rang, the performance was BAD BAD BAD 
After 3 hours of analyzing of our sourcecode we had the solution:
Caching is not enabled by default (suprise surprise... by Oracle)
After adding additionals lines
<jdbc-connection-pool datasource-classname= "oracle.jdbc.pool.OracleDataSource" ...>
<property name="ImplicitCachingEnabled" value="true"/>
<property name="MaxStatements" value="190"/>
</jdbc-connection-pool>
We had an incredible speed up!
The application is now about 10 times faster than before using this DataSource. If it is possible in any case use this Datasource!