So... now that the new fix is in and I'm done sending hate mail to developers... lets talk Arcane... again. Arcane is still one of (if not the) top DPS specs for mage, so lets take a look at it. Last time I spoke about mana regen, lets look at soem other things...
Specs: The primary build is typically some variant of 57/3/11. It's a powerful single target spec. 2/3 in ice shards actually gives it acceptable AoE (And devastating aoE if you can blow some coll downs wih it) The biggest drawback is that it does not bring Improved Scorch or Winter's chill to the Raid. This means that this is the spec for the "second" mage, as your first mage has to bring this buff. THere is a 51/20/0 Arcane spec that can be used, but you will be giving up a numbe of key DPS boosting talents to get improved scorch. Scorch also does not fit into Arcane's rotations very well. So only use this if you have to.
Rotation: Arcane is still a dynamic play style, in fact with the "fix" it is now more of a dynamic style than it was before. For most players you think about what spells do you want to cast. For arcane, the question is more about what spells don't I want to be casting.
Arcane missles, for the most part, is a loser spell. Even talented, it is a loser in terms of DPS and DPM. The only time you want to cast Arcane Missiles is when Missile Barrage procs. Period. End of story. It does however do a lot of damage for one spell. So it's a good candidate for the Arcane Blast debuff.
Arcane Barrage: This is a good spell. It has better DPS than Arcane Blast (no stacks) or Arcane missles but still not as good as AM with Missle Barrage. So with no other buffs, this is your best spell.
Arcane Blast: For he most part, you want to minimize the number of times you have to cast AB unstacked. AB does more DPS as it gets stacked, but of course, at the cost of Mana. It is completely unsustainable fully stacked.
So... What does this mean? Well ideally, you start with Abar, the you'd cast AB until you got a MBarr proc then cast AM. The problem is that is is VERY mana intensive. For a slight loss in DPS, but a huge gain in Mana, go Abar, ABx3. If you get a MBar proc, cast AM. If not Cast Abarr and start over again. This will cost a couple % in DPS but is about 2/3 the mana cost.
So we pick the second one right becasue it's more efficent... right? HA! You forget! This is Arcane baby and we are not locked into just using one cycle! Base the cycle you use on the fight you are in. Got exta mana? Hold out for that MBarr proc and use the first "Burn" cycle. Runnig strapped for mana? Go back to the more efficent version. Still strapped for mana? Reduce ABx3 to ABx2. In this way Arcaen can adjust itself to fit the fight that it's in.