Sadly Mew is gone, he would have become the most used Pokemon being able to counter all those Fighting-type Pokemon in the tier.
I've tested Mienshao and here are my findings:
+I've noticed nothing can really switch in safely into the monster, and it will do at least 20% damage with the combination of Fake Out and U-Turn. Predicting a chandelier switch is even better, as it pretty much always OHKO's the bitch with SE.
+With Snorlax and P2 in the tier, any Fighting type has something going for it. HJK will OHKO pretty much any Normal-type Pokemon as well as severely damage anything else daring to come in.
-Sadly Hi Jump Kick tends to miss which sucks..
-The same about not being able to switch in also goes for Mienshao, it can't switch into anything which makes it a synergic waste of a teamslot. It's a very good revenge-killer and a lead, but that's it.
-There are too many Pokemon that fully counter Mienshao, one of them always being pretty much on any team. Defensive Suicune, Blastoise, Shaymin, Sableye and even physically defensive Roserade can take hits. There is always one of these on opposing teams, at least as how I've experienced the PS! ladder. Sure you're going to say that your teammates can take care of those, but Mienshao just lacks raw power as well as bulk to perform as the star of a team.
After Fake Out/HJK/Stone Edge/U-Turn failed I tried exploiting a Bulk Up set, but even at +1 Defense it's too damn frail. Try to set up with such defenses and you'll end up giving the opponent a free kill.
I tried CB for a few battles, but after that quickly removed Mienshao from my teams. It just isn't what I expected it to be honestly, sadly...
So that's my opinion about Mienshao. I hope it won't become a hype for the sake of the users, you'll see it really sucks.
I personally haven't seen people using Durant or Ditto, but that's probably because the round is still young. I do expect Ditto to become a staple, before it vanishes to the depths of lower OU...