I've been using this Manaphy:
@Damp Rock
240 HP/232 Def/36 Spe Bold
-Surf
-Rain Dance
-Rest
-Calm Mind
This thing seems to be sweeping pretty well, because it can easily find room for setup (bullet punches, scarfed weaker attacks, etc.). This Manaphy is certainly capable of taking down something with it 90% of the time, just because it is so hard to KO after even 1 calm mind, while rain boosted surfs hurt even resists. Of course, like other sweepers (Salamence, Gyarados), this guy needs a bunch of team support. Right now, I have toxic spikes for bulky waters (Vaporeon), a TTar lure (Scarf Latias), an LODugtrio, and 36 speed to outrun TTar on Manaphy. Basically, while this guy can sweep pretty well with relatively few safe counters for him, he requires a bunch of team support, which could detract from being able to take down other stuff (although, Duggy+Latias+Toxic Spikes+Forry sure can handle a lot). I only see this guy being more effective when Garchomp is booted off to Uber (which I'm sure he will) and takes with him half of TTars. When sandstormers are gone, this guy might be too good for OU.
tl;dr: Sweeps very well given team support, interested to see what happens when there is not as much sandstorm flying around (probably not "bad" enough for OU).
Garchomp: Uber- do you see the centralization this guy is causing?
Latias: OU- seriously, she isn't too good for OU, given the past 3 months.