It all depends on your definition of ninja-mined stake, I've seen several with time. I did learn about the mining quite early because the Steemit guys were working in my basement at the time, and after some slight hesitation, decided WTH, I'll mine it and see what happens. The costs were low enough, that it didn't seem like much risk, just labor and computer rental time.
At some point in the future, I'll probably make a post about my history in cryptocurrency in general, including my experiences in Steem. But it's a little off-topic for this post to say much more here, as I'd prefer to keep this post focused on legal discussions about forks.