Get a feel for my tanks gearing and then just DPSed based on my gut feeling and the numbers flashing in front of my face. Never had a complaint from tanks for not taking Omen.
I do rely on macros quite a bit though, example... during BC, I had a macro for equipping my Hunter's Lorekeeper Staff when I use Arcane Shot, and the spirit enchanted Combatant Claymore, and shadowmeld whenever I stopped to eat.