Everyone knows of one version of "The Five Second Rule" that we learned as kids. If you drop a candy bar on the floor as long as you pick it up in under five seconds it is okay to eat. Needless to say it was probably not your mother that taught you this one. There is a different version of this used in the World of Warcraft dealing with your Druids mana regeneration to be aware of...
In WoW the Five Second Rule is usually shorted to "FSR" and has to do with the way mana regeneration is affected by spell casting. One of the ways that Druids regenerate mana is a direct result of their Spirit stat and to a lesser extent their Intelligence stat. Once a spell is cast the regeneration effect you get from your stats does not start again for five seconds. So you are walking along one afternoon minding your own business. A little rabbit hops by and you zap it with a Moonfire. Once that spell is cast you must wait five full seconds for the regeneration effect to begin again. This happens every time you cast a spell with a few exceptions.
1) Those spells and effects that do not cost any mana to cast do not trigger the FSR such as Clearcasting and Natures Swiftness.
2) Those channel spells we use, like Hurricane and Tranquility, are affected by the FSR differently from normally cast spells. The FSR starts in these cases as soon as you begin the cast for one. Secondly the FSR will not go over the five seconds. For example with Hurricane the channel time is 10 seconds. The FSR starts when you begin the channel, and since that channel is longer than 5 seconds you don't have to wait an addition 5 seconds after that spell is complete.
So what's the problem and why should you care? Well, what if you find yourself casting a spell every five seconds for a long fight? That's right! Your little blue bar is empty. A Moonkin or Resto without mana is about has handy in a fight as a lump of dirt.
Luckily there are a few ways to get around this. First of all mp5 gear is not hit by the FSR so regeneration from those sources continues. Also talents like Intensity and Dreamstate are a big help as well as our Innervate spell. While this might not seem like a big deal at the lower or even middle levels once your Druid starts getting up towards the level cap and you get into end game content it becomes a pretty major factor.