I'm jacking a post from Aldriana at EJ about the professions benefits at 3.2:

Alchemy: 80 AP.
Blacsksmithing: 2 epic gems, at 40 AP or 20 of any other stat, meaning your choice of 80 AP or 40 of stat-of-choice (usually Agi or ArPen).
Enchanting: 80 AP.
Herbalism: More healing, handy for questing and soloing stuff, I suppose, but useless in raids.
Inscription: 80 AP
JC: New Dragon Eyes are 68 AP/34 stat of choice, an upgrade of 28/14 over epic gems; thus, the total benefit is 84 AP and/or 42 of stat of choice.
Leatherworking: 80 AP
Mining: 60 sta
Skinning: 40 crit rating

So, among the easily-valued professions, we have a pretty obvious hierarchy:

1. JC: 84, or more if there's a stat with EP > 2.
2. BS: 80, or more if there's a stat with EP > 2.
T3. Enchanting: 80
T3. Inscription: 80
T3. Leatherworking: 80
T3. Alchemy: 80

Okay, so what about the two that are a bit harder to assess? Where do they fit in?

Well, Tailoring gives Swordguard Embroidery, which has a 45 second internal cooldown and a 25% proc rate; thus, un average, it's going to proc about once every 47 seconds, giving it uptime right around 32%; thus, the average-case benefit is 400 * .32 = 128 AP or so. Compare this to the best available alternative, which would be 22 agi for most of us, which has a value right around 45 EP. So the overall benefit is right around 83 EP - give or take. In practice, it might be slightly higher than this, as the proc will tend to align pretty well with your trinket procs, leading to some degree of synergy. Note, however, that as the value of agility increases (and it probably will, with time), this margin will be eroded somewhat.

Engineering, on the other hand, gives a multitude of benefits which we're going to have to add up:

1) Hyperspeed Accelerators now give 20% uptime on 340 haste rating, or 68 average-case haste; this works out to a benefit around 91 EP for Mutilate and 101 for combat; compared to the baseline glove enchant which is 44 EP for both, the benefit is roughly 47 EP for Mutilate and 57 EP for combat.

2) Flexweave Underlay is 1 agi better than the regular cloak enchant. 2 EP for both.

3) Nitro boosts are now identical to Icewalker, with the added benefit of boost movement at need; in an ideal fight, where they can be used on every cooldown, these reduce transit time by 2.5 seconds once every 3 minutes; 1 second of DPS in in the neighborhood of 7000 damage for most of us, so we're looking at something like 17500 bonus damage every 180 seconds, which is a full 100 DPS benefit, right?

Well, no. Because in practice the number of fights on which you need to to move far enough to get the full 2.5 second benefit, and need to do so more often than you can with sprint, are few and far between. The only fight in Ulduar where I can see getting full benefit from them is Yogg phase 2; one can argue you receive partial benefit on Mim, XT Hard, and some modes of Iron Council, but it's definitely the exception and not the rule. And even in those cases, it's only during certain phases, so in reality you'll use them once a fight at most in the majority of cases. So a more realistic assessment is, perhaps, 2 seconds of movement saved across a 10 minute fight, which works out to more like 20 DPS, which is around 25 EP. And on most fights, it will be less than that. So we're looking at, average case, perhaps 10 EP, I would argue.

Finally, we have bombs. A bomb does 1325 base damage, increased 13% by raid buffs, reduced by 6% due to resists, and increased by around 15% due to spell crit. Thus, we estimate the average damage in reality is around 1600; with a 60 sec cooldown, this works out to around 27 DPS, which is somewhere in the neighborhood of 30 EP if used on cooldown.

Thus, the total theoretical benefit of engineering is around 47 + 2 + 10 + 30 = 89 for Mutilate, and 99 for Combat... assuming you use everything on cooldown. If, however, you are consistently 5 seconds late on using Hyperspeed Accelerators, or don't feel like burning through a hundred bombs a night, or otherwise fail to use the profession to it's absolute fullest, it's value is somewhat lower. For instance, if you use bombs and accelerators every 65 seconds instead of every 60, the total benefit drops to 80/90; and every fight you skip using bombs entirely on drops engineering to the bottom of the heap.

So, in terms of optimal professions, what do we find? Well, if you're absolutely commited to using engineering, and use every single ability on cooldown on every fight - including going through very large numbers of bombs and putting up with a lot of extra cooldowns to keep track of - it's going to be the best profession, and thus the optimal pairing is JC/Eng.

However, for those people who aren't willing or able to put up with that level of crap on engineering, it's a weak profession; at that point, JC is the best, and either Tailoring or Blacksmithing will be second. In particular, if there's a stat who's EP value is 2.1 or higher, Blacksmithing is likely best; if not, Tailoring is probably the way to go. However, none of these professions have a significant advantage over LW, Enchanting, Inscription, or Alchemy, so I suspect a lot of rogues will not find it worthwhile to swap professions for the 2 DPS difference between professions.