If you're a tank, you probably have some experience with the way abilities queue up in the live game. Tanks tend to keep their threat-generating abilities on cooldown, and certainly for warrior tanks (I only tank on a warrior or DK), there's a good deal of spam with abilities like Devastate or Heroic Strike. While Cataclysm promises to fix HS spam, the basic form of tanking remains, and reliable threat abilities will be spammed. The difficulty will be in the new way abilities are queued up when you hit the button for that ability. It seems that a few exploiters have caused a change that may affect you.
The issue here is not the queue system itself but rather being locked into a choice when you rely on proc abilities that you can't predict. In the absence of a Sword and Board proc, for instance, or Revenge lighting up, you're going to want to use an ability like Devastate or Heroic Strike to generate threat, since some threat is always better than no threat. But when a higher-priority attack like Shield Slam or Revenge lights up, the last thing you want is to be locked into Devastate, unable to use the greater threat ability not only until Devastate fires but until the global cooldown -- which could end up costing you over 2 seconds on a proc that has a limited duration, as well as costing you that threat. There's a similar issue for DPS or PvP players, of course. A high-damage proc ability like Bloodsurge could very well fall away entirely while you're waiting for your ability queue to clear.
Hopefully that override will be in place soon. At any rate, this is something to be aware of for the immediate future.