For now, I think the only possible use we could have for black holes is to use them as gigantic garbage cans. Instead of dumping our trash in ever growing landfills, we could just sent it all into a black hole and be done with it.  Could even get rid of all that pesky nuclear waste. No fuss, no muss. wouldn't be cheaper to recycle it instead of the humongous cost of launching it into a black hole?    What about the black hole aliens getting pissed off at us for dumping our thrash in their homeland? :p