I heard its dense, hard, stable...so it would be good at least for a lamination?

I imagine it's hard on tools, so if anything I would guess that that's the reason you don't commonly see it as a neck wood, too much carving involved. If you're looking for something with those properties to use in a neck, I'd probably suggest purpleheart.

I was thinking more like a 3 piece neck, 2 big sides of maple, and a thin center of pau ferro.

Purpleheart is harder than Pau ferro IMHO. I've used it for neck stringers several times it works about the same as most exotic hardwoods.

I used Cocobolo in a neck and that was somewhat hard to work with. I agree with Scott on this one, Pau Ferro is not that hard to work with. Id say go for it. Some people use Ebony in necks so why not?!?

Ken Smith uses pau ferro laminations in his maple necks. He refers to it by one of its other names, Morado. And you probably don't get a more stable neck than on a KS (based on never hearing or reading a single neck complaint over many years).

Purpleheart is loaded will silica and is harder on tools than pau ferro. You probably don't find it in necks as much because it's more expensive than alternatives and generally there's less of it at the wood store. Jack Read used to use it in some of his necks, it's a great wood that works quite well with sharp tools.

Thanks guy! The Ken Smith piece of information made me feel assured.