Load balancing to distribute workload across multiple nodes in a cluster works with RAP out of the box since version 1.0.
One thing to mind though when setting up a load balancer for RAP applications is that it must be configured to use stcky sessoins (aka session affinity). This entails that once a session is started, the same server serves all requests for that session.
For information on how to set up load balancing, refer to the servlet container documentation. E.g. Tomcat
Transparent session failover
Development takes place in HEAD, if you are interested you may want to directly check out the source from the source code repository. To run the tests you will have to add Jetty 7.4 and the H2 embedded database (version 1.1) to your target platform. Nightly builds are also available and can be downloaded from the build server.
We plan to ship a first version with Milestone 1 of RAP 1.5 which will be available end of August 2011.