NOTE: This question is from 2014. As of Java 11 OpenJDK and Oracle JDK are converging.
Are there any crucial differences between Ora
Aside from the obvious licensing difference, the major difference between OpenJDK and OracleJDK 11 are stability and performance updates.
Source: https://www.youtube.com/watch?v=Adv9--6IcQI&t=385
Every 6 months the two codebases will be in-sync. But during the 6 month window OpenJDK will only receive security updates while OracleJDK will receive additional stability and performance updates.
Given that update releases only occur every 3 months for both OpenJDK and OracleJDK this means that you are missing out on (at most) 3 months worth of fixes until the next major release comes out and you upgrade. However, if you choose to stick to LTS releases then a commercial license begins to make more sense.