A very important benefit of using Infinispan's Externalizer framework is that user classes now benefit from a lightning fast marshalling framework based on JBoss Marshalling. Back in the 4.0.0 days when we switched from JDK serialization to JBoss Marshalling, we saw a performance improvement of around 10-15% and we're confident that 5.x user applications will see a similar performance increase once they start providing Externalizer implementations for their own types.
At this stage, it's very important that Infinispan users have a go at implementing their own Externalizer implementations so that we have enough time to make adjustments based on feedback provided. Your input is crucial!!
Staying with the marshalling topic, another novelty included in this release is the ability to plug Hot Rod clients with portable serialization thanks to Apache Avro. This is not tremendously important right now, but once Hot Rod protocol clients have been written in other languages, they'd be able to seamlessly share data even if they're written in different languages! In case you're not aware, a Python Hot Rod client is already in the making...
Finally, details of all issues fixed can be found here, the download is here, and please report issues here. :-)
Enjoy and Merry Christmas to all :)