This was in some of the earlier iterations of
http://drupal.org/node/111127 - the issue is that one rogue contrib module could completely disable node caching on a site by setting this flag. With _load() and _post_load() the worst that happens if you get them confused is you end up with some stale data or a single module not taking advantage of the cache as well as it could.
Either way, would be really great to have some more reviews of the issue itself, since it's been sitting at RTBC for a while, and discussion on this list doesn't get taken into account on the issue queue.
Nat