Hinted Handoff is an optional part of writes whose primary purpose is to provide extreme write availability when consistency is not required.
Secondarily, Hinted Handoff can reduce the time required for a temporarily failed node to become consistent again with live ones. This is especially useful when a flakey network causes false-positive failures.
Hinted Handoff is not a replacement for repair mechanisms.
Stonebraker is conflating application needs with database support. That's broke. I need a certain set of characteristics from my application, I can and probably will satisfy them with a collection of components which will include some storage and some custom code.
No one in their right mind would use a database as a cache even if it were a "main memory database".
A decent architecture has layers of responsibility, many of those are not for the storage infrastructure to manage. This is because the storage layer can never have enough of the overall application context (usage patterns etc) to make the right decisions at runtime.
links for 2011-06-01