[JMT]

The increased estrogen can have an effect on your equipment, including shrinkage and a lower libido. I understand that over the long term it can also result in sterility. I haven't read anywhere yet of it resulting in permanent impotence though (if by impotence you mean the ability to have an erection). When you take a break from it, things should function better, or you could try some of the other herbals designed for that purpose (read bryony's posts about Butea Superba).

Also, if you look up HRT MTF on wikipedia there's a good bit of information.