In OU he faces obvious competition from Infernape, Blaziken and Hihidaruma (no Emboar..), given that they all have similar roles.
Arcanine's pros are that he is technically the bulkiest, although SR weakness mitigates this somewhat compared to the part fighters, and gets Extreemspeed (The main reason for using him I believe), Wild Volt and Morning Sun. STAB on Close Combat isn't really needed, he's only targeting Blissey / Chansey / Tyranitar / Sazandora and possibly Zuzurikin and they are generally OHKO'd anyway, and Wild Volt deals with the majority of Bulky Waters (run from Swampert).
However Infernape and Blaziken are faster, have higher mixed attacking stats, access to effective stat boosting moves (no Howl doesn't count its almost entirely pointless), Infernape has a better movepool with Mach Punch, Thunderpunch and Grass Knot and Blaziken has Speed Boost and Baton Pass. Hihidaruma is just a steamroller with huge base Attack and Encourage to boost Flare Blitz and Rock Slide, as well as Superpower and U-Turn to complete him.
I suppose its a personal choice, but he does seem somewhat outclassed as a sweeper, and is too easily countered by stall in Swampert and Hippowdon and in offense by the multitude of fast Dragon types that are on almost every team. I really can't picture him being heavily effective, but he is still very usable if you just think he's bloody cool.
Seems to be headed for BL now Milotic falls to Wild Volt and Rhyperior to Close Combat. Quite annoying really, we'll never see him in competitive play again...