We plan tu upgrade, we just need to do it and test it :)
I'm glad to see that the changes are minor, the changelog was quite scary related to the Hibernate persistence and nobody took the time yet to do the upgrade.
I have load tested with JackRabbit 1.1.1 and its fully compatible (no code changes necessary)
1.0 had a lot of memory leak, but they are all gone in 1.1.1
I did the upgrade to 1.1.1 just before 1.2.1 came out, yes it was fully backward compatible.