I addressed this briefly in my 3.0 Ret FAQ, but the problem persists across the Warcraft universe. The issue came up briefly on Maintankadin, with notable MTadin moderator Lore weighing in with his experiences. Here's the exchange, from this thread:
Rasmfrackn: Picking up int is improving your dps. It has to be because Ret is apparently intended to be resource limited and making choices about what to spend its mana on. If the int comes cheaply enough, it's an improvement.
Lore: I've been mentioning this a lot lately: I spam consecrate on every fight. Exorcism too where I can. I push 3200 DPS raid buffed. I have only come close to running out of mana once or twice, and I have never come remotely close to running out of mana after popping a runic mana pot.People, people, people. Please understand: if you're running out of mana, you're doing it wrong. What Lore said is the truth: there is no need to gear for Intellect! Here's a checklist of things to do to make sure you have enough mana to keep chugging along:
- Bring mana potions.
- Use Divine Please once you hit 70-75% mana and then every cooldown there-after.
- Prioritize Judgement to make sure you get the JotW mana kick-back every chance you can.
- Use Avenging Wrath every time the cooldown is up.
- Gear yourself correctly so as to maximize your damage output (do enough damage and you'll hurt yourself more with SoB/SotM, get more mana from heals - get strength, hit, expertise, and crit. This is why you want to use wings every cooldown as well).
- If you're desperate, bring Dark Runes or Demonic Runes.