"If an Arcbound creature gets enough -1/-1 counters to make its toughness 0 or cause the damage on it to now be lethal, the Modular ability will still give another artifact creature a number of +1/+1 counters equal to the number the Arcbound creature had before it got -1/-1 counters."
...so if I give an Arcbound Crusher (Modular 1) Persist by activating Cauldron of Souls, and it dies to something, when it persists, it will return to the battlefield with one +1/+1, one -1/-1 (due to persist), and die again - but modular will trigger again and I'll get to put one +1/+1 counter on a creature?
That's really kind of crazy when you think about some of the interactions. Thank everything holy they didn't print a card with "creatures you control have Persist", or you could bounce modular guys infinitely.
--Kasreyn