As far as I know, the following people are using the OS Giken Cross Mission gearset:
LeeWah
Ben (RPM GTR)
Emre
I think Frank may also be using one but that's only what I've heard.
It's an awesome box. It been out dragging with me at full power (600+awkw) and not missed a beat.
If you treat the box right, it'll hold for sure.
BTW, don't trust the Trust boxes. Ben has smashed a number of gears in previous Trust boxes before he moved to the OS. Since the change, he hasn't busted any gears to the best of my knowledge.
Well worth the investment IMO.