On your download page http://jdbc.postgresql.org/download.html
You specify that the JDBC3 is compatible for JDK 1.5 and if we are using
JDK6, we should use JDBC4.
But, in my case, I'm using Tomcat6 (the connection pool is JDBC3) which
is running under JVM 6.
Therefore, your driver JDBC4 does it validate to run on a JDBC3
connection pool.
Regards