Yes, I tried opine.

It's decentralized, which is nice. But it needs to have enough people using it.

I've only tried it once, on the beared (or non-bearded?) scientists post.

Tribe.net works for me, I've gotten quite involved over there.

It's problem is pretty much the same as opine -- if BoingBoing-pere does not promote it in general, it will have a quiet, lingering life. Not quite dead, but exactly alive. The Tribe.net discussion doesn't thrive, but it isn't dead, I think, mainly becuase of all of the other tribe.net traffic. But the opine-option does not have side-traffic, no way to stumble upon it, or save it, no reminders by seeing it in a list of some sort.