Has there been any word yet on a possible PSN release?  I know this game is said to be a cash-in.  But it looks like a fun cash-in to me. 
oh yes it's really REALLY fun!   

I think it's possible for a PSN release, but I think Konami's plan might be to focus on the 360 version and get the DLC done right, and with these recent problems they have been having, it might have delayed their PS3 plans.  But I'm sure there is a good chance Harmony of Despair will be released for PSN after 360 version gets all or most of the planned DLC released for it.  
It would be a waste if Konami doesn't sell it on PSN too, because they could make even more sales out of it.
And a Konami employee and IGA himself said that if the 360 version sells good then a PS3 version is likely to happen. As far as I heard, about 70,000 bought Harmony of Despair, which is pretty good for a digital market title. 
http://www.gamasutra.com/view/news/30301/InDepth_Xbox_Live_Arcade_Sales_Analysis_August_2010.phpand those stats were only counting the single player.  It sold slightly more than Tomb Raider and Scott Pilgrim the first month. 
By now, those numbers total are even higher.  
Here is a September article:
http://www.planetxbox360.com/article_11798/Xbox_Live_Arcade_Sees_Best_Month_of_Sales_Ever_in_August"Konami's 'Castlevania: Harmony of Despair' was in second place with 
131,000 units sold"
I would say it's pretty successful.   Maybe Konami will announce the PSN version sometime next year after they get their act together to release the rest of the 360 DLC?