the POI algorithm, albeit unique, is not a huge amount different than a regular POS algorithm, the only difference being that it takes into consideration how many transactions you make.
If you think it can easily be cheated, well i guess all you need to do is move your funds across different accounts constantly.
Thanks for confirming it is just proof-of-stake with some weighting by the transaction graph. That is my read also:
http://nem.io/NEM_techRef.pdf#section.7As for whether it's security could be gamed (leading to The DAO like failure), well I would argue that the risk is nonzero (given that anyone can make a lot of transactions) until it has been properly peer reviewed. You can't trust one guy to do this sort of analysis.