One of the main problems I've heard is that the motor itself is a giant degauss-er that even the strongest magnets are not immune to.
That is why I think it important to first and foremost run one into the ground and see why it stops working before building a bigger one.
It may very well be that any energy output you see is from the magnets losing their potential.
http://freeenergynews.com/Directory/...nt_keep_rating
"...
says he saw the Perendev motor running, and that his group has built two different working magnetic motor designs, including one that is analogous to the Perendev, but that they all depleted their magnets under load...
the energy consumed in the overall manufacturing process is 20-25 times the energy you will get out."