I'm in the "thinks it's great" camp. It does what it's intended to do: tone down the use of instakill without eliminating its usefulness or viability. And, it does so with some elegance. I think it will take some tweaking to balance the penalty...but the mechanism is essentially sound. It scales. It leaves real benefit to achieving the uberest of dcs. It doesn't require saves or resists being raised to the point that newer players are utterly incapable of playing as PM. And, it lets you use the spells whenever and wherever you want....without spamming them. Wizards are supposed to be tacticians, "haunting" requires tactical play.
It's interesting that a lot of the same players who were asking "why not just increase mob saves" in the HtK thread are the same ones demanding there be a hard cap on haunting. You'd almost suspect that they were planning to game the system, shoot for 60 or so dc on the assumption that would enable them to continue with exactly the same play style that's created the need for change to begin with.*shrug*
It might be more constructive for the players to start thinking about what they might like to see in the upcoming enhancement revamp. It seems to me there's a lot of possibility in terms of enhancing options for PM in particular beyond simply cycling through CoD, WoB and FoD. Like making those skele summons useful?