I feel this deserves a mention:
A lot of Ubers focus on outspeeding other Ubers. In a rush to boost speed and an attack stat, the otherwise credible defenses of many Ubers are left untouched, making them more susceptible to attack.
Where am I leading this to? Trick Room.
On one of my Uber teams I run a Trick Room Mew. I imagine Bronzong could also work, to a lesser extent.
Anyway, with Trick Room all of a sudden the 252 Speed spreads become worthless for a few turns. Its as if they were only given 256 maximum EVs. Meanwhile, your slow Ubers can focus on building HP or a defense while maximizing an attack stat with a boosting nature. Basically replace OU Rhyperior with Groudon and that's the effect.
In short, Trick Room is dangerous to Ubers. A lot of them rely solely on speed to be effective.