With greenpois0n, what exactly happened? The first time I tried it, there was a point at which text was scrolling down the screen and then it stopped for several minutes with what appeared to be a serious error message, at which point I panicked and rebooted. When I tried again, I waited it out at that point in the process, and eventually the scrolling continued and the jailbreak completed. I don't know if the current revision of greenpois0n does that; I think I was using the previous one.