I noticed quite a lot of rare black weapons that are crafted on people's profiles, what do you guys think, is it worth spending let's say 10mil on some crafting?

Crafting like that is a just another form of gambling.
It might work out, but personally I doubt it.

The reason you see a bunch of crafted items might be because of a new crafting exploit. At least that's what I've heard. I don't know how it was doing, but whoever did it recently decided to post all their stuff up and cash in.

And what do you know, my wizard has one of them haha.

Yeah back in Jan (i think? there was a topic on it here somewhere) the AH was flooded with crafted items all almost exactly the same or very similar. It was patched but people still have the weapons :)