Chris Jones has posted some "pictures" of the performance that an Oracle database sees when it uses the connection pooling versus the normal connect/allocate sort of connection with the Oracle OCI8 driver for PHP. As you can see, the differences in memory consumption are huge.
Here is a screen shot from a PHP OCI8 connection pooling demo that I like to run. It graphically shows how little database host memory is needed when using DRCP connection pooling with Oracle Database 11g. Migrating to DRCP can be as simple as starting the pool and changing the connection string in your PHP application.
He also describes the differences between the pooled and non-pooled connections (to the developer it's as easy as putting ":pooled" in the connect string) in his graphs, and notes that using the pooling doesn't just have to be for large site - smaller sites can benefit too.