Hi Jona. I've been at least 51 points in Arcane since 2.0, and while I haven't hit up Gruul or Mag raids yet, I've been through Karazhan so many times that I could likely do it with my eyes closed.
http://armory.worldofwarcraft.com/ch...her&n=Sinazeel is my Armory profile. My Riding Crop is currently in the top slot, but that's usually a Lightning Capacitor, if you want a good feel of my total gear.
Well, I don't think your gear is all that great. I'm gonna echo the sentiments earlier on that you need to invest a bit more in stats. Stamina is going to help keep you up more, especially with most of the tBC content eschewing the traditional tank&spank fights and going for fancy AoE crap. It allows some leeway with fights, since you'll be able to screw up once or twice and not die. As the saying goes, a dead mage does 0 dps. Intellect is fantastic, since having tons of mana frees you up a bit what you can do, and it will also be increasing your crit chance and damage. To that end, I feel that the tailoring BoE sets don't have much to offer for an Arcane mage. There's a notable lack of stats on Spellstrike, and +hit isn't that high a priority due to Arcane Focus. Battlecast isn't too shabby, and is likely cheaper to buy, but the lack of crit is very meh. Spellfire however, is incredible and the lack of stats on those pieces is just fine, though I'd lean toward putting Stamina gems in every blue socket I have. Also, I personally avoid using gems in their non-syngeristic slots, but I suppose the whole socketing thing is to do what you want with gear.
In actual fighting, I've found that I rarely need to actually use non-Arcane spells. I usually use a AB+AB+AM rotation. My latency/whatever lets me get off the next AB right after the debuff wears off, but while still using the shortened casting time. If I'm trying to conserve mana, I'll do a single AB instead of two, and if I'm REALLY trying to conserve mana, I'll do AB, Scorch x3, then repeat. While it seems obvious, try to use AM when you Clearcast. Same with your rawr-Pyroblast macro. This will help offset the higher mana cost of AM.
If you're having trouble with mana, try using Mage Armor instead of Molten. Yeah yeah, we all love the crit bonus, but it does you little good if you're sitting there oom. Also learn to chain consumables. Even if you're spamming AM (very high -mana per second by doing that), it'll take you a minute to go oom. Evocate, then start chugging mana gems (make the highest three ranks you have) and mana pots. Once I've gone through a fight a few times, I find that I learn how to better conserve my mana (don't start AM if Moroes is about to vanish or Prince is about to Nova, etc).
Ohhhh, one more thing! Go hit the auction house and start looking for a bunch of green staves or daggers+offhands, and a wand, of the Of Spirit variety. Install Itemrack or something of that nature, and make a set to switch out that stuff. Throw them on before you start using Evocation for another thousand or two of mana. It really helps make it not suck so much.
Arcane mages really pick up once you start factoring in buffs from other players. Paladins are awesome for this, especially Protection. BoW is fantastic, as is Kings. Salv isn't much of a priority, but can help if your tank is learning/sucks/isn'tProt. JoW is where it really shines, since each volley of AM can (and often will) proc the mana gain from JoW.
Warlocks might be viewed negatively my some mages as competition, but an Arcane Mage counts as benefitting from Curse of Shadows, and helps to convince others of using CoS instead of CoA or whatever. Shadow Priests are also useful for this, with Misery increasing damage and VT feeding mana back into you. SPriests gain about as much from Salvation as you will from JoW; With both of them, you can actually almost even out your mana gain and mana usage.
Disc priests are nice as well, what with the Divine Spirit boosting normal mana regen and Evocation. Imp DS isn't that much damage, but anything is better than nothing. Just make sure they don't try to PI you when you're about to pop AP, since they don't stack.
Shamans are very good, but only if they're a castery-type as well. Windfury is crap for us, sadly. Wrath of Air grants the largest bonus, due to AM's favoring of straight damage. Totem of Wrath is pretty cool if you can find someone specced in it. BM hunters are nice as well, since Ferocious Instinct works on ALL damage.
Consumables are very good. I'd shell out for the new Wizard Oils, along with some Adepts and Draenic Wisdom pots. Until you get more Stamina I'd use either the 20 Sta/Spirit food buffs or the Blackened Sporefish (20 STA and 8 mp5). After that I'd use the spell damage foods if you don't expect to take much damage, but damage intensive fights (such as Netherspite's aura or if you're tanking the imps in Illhoof) would see priority to the stamina foods.
Lastly, I'd consider respeccing a bit. Yeah, I know you don't want to, but that's why I'm listing it last. I'd sooner take Impact than Imp Fireball, and put points into Ignite instead of Imp Fire Blast. I might also consider not bothering with Pyroblast, since you're basically spending a talent point for another 200 damage on your rawr-macro. Not to mention that using Fireball as a replacement isn't that bad, as long as you don't have the reducing coefficient from Imp Fireball.
Good luck out there raiding. In general, it doesn't matter that much about how you spec, as long as you enjoy playing your character. It'll give you incentive to play well and such. Remember that the guilds that got Kel'Thuzad down first were Horde guilds, when the popular opinion was that Paladins made raiding 'easier'.