In our case, we tried upgrading to 2.3.40, and we had a crash of a sort that has not been seen before, at least not very often. We've stepped back to 2.3.35 because we know at least something of what caused the failure there, and we know how to avoid at least that particular problem. We're still working on the details of exactly what is going wrong and why.
While I admit it's very hard (and very important) to retain a good S/N ratio...
One of the great things about using community software is that we can all help each other out, either directly ("we've analyzed this and found X") or indirectly ("we've noticed Y three times, which never happened before, just FYI for now" for pattern development), by sharing our progress in these matters. If you have anything of this sort to report, I'm sure it'd be welcomed here or in -devel as appropriate.