I LOVE this macro:
/script DEFAULT_CHAT_FRAME:AddMessage("Need 102.4 combined avoidance. Currently at:",0.8,0.8,1)
/script DEFAULT_CHAT_FRAME:AddMessage(GetDodgeChance()+GetBlockChance()+GetParryChance()+5+(GetCombatRating(CR_DEFENSE_SKILL)*150/355 + 20)*0.04,1,0.5,0)
Got it from elitist jerks. When trading gear around and switching enchants/calculations, this macro is a godsend.