"How hard is it to crack passwords stored using this technique?"
Suppose that three people have passwords that are each randomly chosen and 6 characters long. A typical laptop can crack those passwords in about 1 hour.
If you take the same passwords and protect them with PolyPassHash, every computer on the planet working together cannot crack the password in 1 hour. In fact, to search the key space, it would take every computer on the planet longer than the universe is estimated to have existed.
If it sounds too good - it probably is. Can anyone with a strong cryptography background explain if this idea has merit or if it is simply pixie dust.