We've been using the host node map recently, and it has numerous bugs. It's badly integrated with ad_conn, and the primary key was on the wrong field: you could have one host pointing to multiple nodes (that makes no sense), but no two hosts pointing to the same node (which might make sense). We've fixed some of these bugs (specifically Eric has), and we're working on more general solutions for the rest. The moral of the story, though, is that host node map seems to be poorly built and not really used - probably needs a revamp. The small fixes Eric and I have added make it somewhat usable, but we're still a bit worried.
