I really didn't want to do this, but it looks like a 5.1.1 will be necessary.  The biggest (critical, IMO, for 5.1.1) issues I see are:

1. https://issues.jboss.org/browse/ISPN-1786 - I presume this has to do with a bug Mircea spotted that virtual nodes were not being enabled by the config parser.  Which meant that even in the case of tests enabling virtual nodes, we still saw uneven distribution and hence poor performance (well spotted, Mircea).  

2. Related to 1, I don't think there is a JIRA for this yet, to change the default number of virtual nodes from 1 to 100 or so.  After we profile and analyse the impact of enabling this by default.  I'm particularly concerned about (a) memory footprint and (b) effects on Hot Rod relaying topology information back to clients.  Maybe 10 is a more sane default as a result.

3. https://issues.jboss.org/browse/ISPN-1788 - config parser out of sync with XSD!

4. https://issues.jboss.org/browse/ISPN-1798 - forceReturnValues parameter in the RemoteCacheManager.getCache() method is ignored!

In addition, we may as well have these "nice to have's" in as well:

https://issues.jboss.org/browse/ISPN-1787

https://issues.jboss.org/browse/ISPN-1793

https://issues.jboss.org/browse/ISPN-1795

https://issues.jboss.org/browse/ISPN-1789

https://issues.jboss.org/browse/ISPN-1784

What do you think?  Anything else you feel that is crucial for a 5.1.1?  I'd like to do this sooner rather than later, so we can still focus on 5.2.0.  So please respond asap.