I remember hearing about Mas Oyama training with makiwara to the point that he couldn't straighten his hands -- they were turned into weapons, but they no longer had the full function of hands any more.
My karate teacher was pretty famous for his ability to break things. There were very impressive pictures of him around the dojo, one in which he was breaking a stack of three one-foot thick ice blocks. His hands, too, were quite gnarled, although still (somewhat) functional.
I prefer to keep my hands as they are -- hands. I don't care to make it into a "weapon" of any kind. Sure, at this point, I could probably hurt someone with my hands, but it's becauce I've learned (to a point, at least) how to use my entire body in doing so -- just like the rest of aikido.
One of the senior students here warns about the misconception that we have to train differently in practicing aikido weapons than what we normally do in empty handed practice. Both are there to cultivate the same principles.
Lastly, some koryu folks I know believe empty-handed training derived from weapons training rather than the other way around...