I just found out about these today:
http://www.randallamplifiers.com/Cabine ... ation.html
http://www.jlhproducts.com/axetrak/
The write-ups on these make it sound like they're designed for professional use, but my guess is that these things are marketed towards home-musicians who have some anxiety about needing to record loud, and not wanting to trust amp/cab sims.
It sounds like a neat idea, but I can only imagine how limiting this is on a person's tone. Sure, stick an SM57 in the box right near the cone, but how does it make up for not being able to place a large-diaphragm condenser a bit further away to help capture what a close dynamic can't?
Anyway, I just wanted to throw this out there and see what you guys thought about them.