I would have to disagree with a Teratoma being the worst type of tumor to have (albiet in ones brain of course it could present some serious issues) considering they are mostly benign and very treatable. And on the cool factor you can find some rather interesting things inside of them. I should also say gross factor, as most people do not share my ideas of what is 'cool'
I would wonder how long it would be until we can be absolutely sure that we have successfully reprogrammed these cells. I'm not sure that is possible at this point, though someone feel free to correct me on that, as I am not sure of the process.