Ha, I wanted to say what Bologo said, but I didn't know how to put it into words. xD
Well, I think Flareon would be most effective as an OU wall-breaker. At least some of them. Let's look through a small list, shall we?
Cresselia: Its normal moves do relatively little to Flareon, and it can use Yawn to prevent it from boosting with Charge Beam. While Bite and Leer are situational, in this case they get the job done. Base 95 SA isn't bad either, so it just use Shadow Ball and Fake Tears is also an option. Flareon can also use Wish for recovery.
Bronzong: Flareon, even with its poor speed, will outspeed Bonzong and will proceed to Yawn it and force a switch. If it has rest, Flareon can then proceed to Sleep Talk Fire Fang or Flamethrower until it dies. I haven't done damage calcs on either, since Bronzong will often carry Earthquake. If you do not wish to carry sleep, Flareon fortunately gets burn baby burn WoW to remedy its poor defenses. Such a shame it doesn't get Taunt.
Spiritomb: Not OU, but getting there. xD The standard set, iirc, is HP Fighting/Dark Pulse/WoW/Pain Split. A correctly predicted switch on the WoW, and gg Spiritomb, since the only thing it can do is Pain Split. Fortunately, Flareon gets Wish so it can set up on Tomb and shake off any damage.
Skarmory: I haven't done any calcs and this thing outspeeds Flareon. Ha. >_> It's really STAB Brave Bird vs STAB SE Flamethrower/Fire Blast. Some EV's into Defense and Speed should do the trick.
Blissey: Flareon outspeeds Blissey, so it can set up a Sub before Blissey can status, set up, and gg Blissey.
Celebi: The worst it can do to it is either Toxic or Perish Song.
Jirachi: The worst that I can think of atm is Toxic.
Forretress: Lawls.
Yes, there are many other things that can kill Flareon in OU but the rest of the team should be prepared for it. Nothing can counter everything, so the properly set up team can utilize it effectively. It screams for a few moves, but in no way is it 'unsalvagable' as someone has suggested. In fact, I wouldn't call anything with an attack superior to Heracross, Gyarados, Electivire, Donphan, and Weavile, and equal to Garchomp, Ho-oh, Breloom, Mamoswine and Machamp 'unsalvagable'. Its special defense and even HP are better than Spiritomb's, as well as its SD being superior to Gyara's (and with no 4x either) and of course Jirachi. Sure, it's not as fast as everything else, and its defenses do not constitute a tank, but on a properly constructed team, it can do well. And the use of Moltres tell you that SR weakness isn't a huge problem. Also, the people who say that Flareon will not improve even if it has a better movepool---Arcanine can't take that much of an advantage of its movepool like Flareon can. It doesn't get Baton Pass either. It's stats, in a way are too balanced---it's not particularily extraordinary in any one area, and that's why I never took a liking to it. Even a mere Leaf Blade would greatly improve Flareon, and it'd be perfect if it got Crunch. Base 95 SA isn't terrible either, it'd work great as a mixed sweeper.
@Mood: I want you to look at my Trick Room team in the face and say that. That's absolutely untrue.