The following is the basic stat priority for Arcane Mages:
Hit Rating (to cap - 1742 or 17%)
Spellpower (Only applicable on main hand/two hand weapons, outdated enchants and some trinket effects)
Haste (to soft cap - see below)
Haste (after soft cap)
An Explanation of Stat Priorities
It is worth noting that stat priorities are a guide intended to help you select your gear upgrades, enchants and gems appropriately. You must exercise common sense when applying this as they can sometime vary depending on raid composition (and corresponding buffs), your gear and your playstyle. I do like to stress the playstyle part because some Arcane Mages perform much better with stacked mastery over the stacked hasted to soft cap, so you have two options here; play to your strengths (good dps) or practice to improve your playstyle (dps loss whilst you're practicing but an overall dps increase when you've mastered it). It can also sometimes vary by encounter but personally I rarely alter my gear specific for one encounter. So what do I mean by application of common sense? Well sometimes it is easy to become blinkered by stat priorities which can lead to some very stupid decisions. For example; deciding not to take a very clear gear upgrade because it has a very slight reduction on intellect, even though it massively boosts your haste and mastery. Although intellect is your best stat overall, the dps gained from a big increase to both haste and mastery would far out weigh a minor loss in intellect.
Intellect; this is your best statistic. It scales extremely well for all mages and particularly for Arcane.
Hit Rating; this determines whether you hit or miss your target. Do not neglect your hit rating for intellect, it is still your second most important statistic up to the cap and it is vital you reach this point or as close as you realistically can. The cap is the point where you can no longer miss the target. As raid bosses are considered to be three levels above your level (ie. 88 at present). it means you you start out with a 17% chance to miss any spells you cast against a raid boss. That's a pretty big chance to miss. Therefore you need to close that 17% gap by reaching the cap of 1742, which means you will always hit. Any points over 1742 are effectively wasted because you cannot improve on a 0% chance to miss. I wouldn't worry if you are a little bit over and I wouldn't worry if you're a little bit under but try to get as close to this magical number as possible. Sites like Rawr and Mr. Robot will help you close that gap. Generally if I have a choice between being under by a bit or over by a bit I'd go under by a bit. The last thing I would say about hit is try to avoid gemming for hit (gem for int instead) and try to avoid using trinkets to reach hit unless it is absolutely unavoidable (and if it is unavoidable, try to replace them as soon as you get other gear to boost your hit rating). The reason for this is that you will get far better DPS from Int Gems than Hit Gems, similarly trinkets can be very powerful items often with large static increases in valued stats like Intellect or Mastery so try to avoid using trinkets for hit, you can easily reach the cap with some careful reforging of crit or excess haste stats instead.
Remember, if you're not raiding and only doing heroic dungeons then your Hit Cap is only 4% because mobs and bosses in Cataclysm heroics are level 85 (the same as you). You don't need to push for 17% Hit if you aren't raiding.
Spellpower; this determines in a large part how much your spell will hit for. It is mostly governed by your intellect score and the spellpower score on your main hand weapon. Some trinkets will have effects (either activated by 'using' the trinket or by random chance called a proc) which will also increase your spellpower. It is primarily included to help you make decisions on weapons and trinkets so that you know its relative value.
Haste & The Soft Cap
So what is the 'Soft Cap'? The best way to describe it is the point where the value of the statistic reduces after reaching this point. This is different to a hard cap (like hit rating) because excess points in the statistic over the cap don't become valueless, just less valued (or less effective). Similarly, soft caps tend to be less cut and dry compared to hard caps and can change depending on a variety of different conditions including buffs available and the gear you're wearing.
So what's the soft cap for haste as an Arcane Mage? Generally it is agreed to be the point where the cast time of Arcane Blast becomes 1 second when Bloodlust or Time Warp is active. This is because your Global Cooldown (GCD) can never be less than 1 second. For an extreme example; your haste is so high you can cast Arcane Blast in 0.5 seconds during a Bloodlust, you still can't cast your next Arcane Blast for another 0.5 seconds, therefore all those extra points in haste are effectively useless during this time because no matter how low your cast time of Arcane Blast you can still only cast one Arcane Blast everyone 1 second. However, the extra haste is not completely useless (like in a hard cap) because Bloodlust is only a 40 second period of the fight, so you'll still be benefiting from that haste outside of the bloodlust period, overall though it's just not as valuable as it was before hitting that soft cap.
"Cut to the chase Runz, what's the number?"
I must admit, I didn't calculate these numbers myself. They're the work of the fantastic AceRider on Elitist Jerks, click the link if you want to have a nosey at them yourself. NB. All of these calculations assume that you have 3/3 in Netherwind Presence, cos if you don't you're probably doing it wrong.
With the 4pcT11 bonus;
Hard cap = 5097 rating.
With 5% = 4252 rating.
With TW = 961 rating.
With 5% and TW = 308 rating.
Without the 4pcT11 bonus;
Hard cap = 7082 rating.
With 5% = 6134 rating.
With TW = 2498 rating.
With 5% and TW = 1768 rating.
Goblin with the 4pcT11 bonus;
With 5% and TW = 2.4% or 181 rating.
Goblin without the 4pcT11 bonus;
With 5% and TW = 13.8% or 1624 rating.
The 5% buff comes from other members of you raid, you'll get it from a Shaman (Wrath of Air Totem), Moonkin Druid (Moonkin Aura) or Shadow Priest (Mind Quickening). TW stands for Time Warp, also means Bloodlust. 4pcT11 is the bonus received from having four pieces of the the Tier 11 Mage (Firelord) gear.
There's a little bit of quibbling over the math applicable to certain conditions, but as long as you're between 1400 and 1800 haste (or 300 to 500 with the 4pcT11 bonus) you're in a good position with 1768 being the golden number to remember.