Shiv

Actually, the energy used is entirely dependent on the speed of the offhand.

20+(10*weapon speed) = Energy consumption

So, with a 1.8 speed offhand:

20+(10*1.8)= 38 energy

This move is much more useful than most people realize.

Every rogue can use Shiv for utility. You have the option to instantly apply the poison of your chioice instead of having to wait for it to proc from auto-attacks. A nice option to have when necessary. But, it goes beyond that...

Think about a Hemmorage spec. Beginning rogues look at Hemo, and they see the "increased physical damage" part... without realizing that the real power of Hemo is that it is an instant attack, costs only 35 energy, and gives a combo point. You spec Hemo, and it becomes your main attack.

Now there's a new spec going around-- Shiv Swords.

I met a fellow rogue the other day who was dual-wielding Revengers:
http://www.wowhead.com/?item=28311

I asked him about the proc rate, and he said it was not great, but decent, like a Crusader proc. Then he went on to tell me about his spec-- he had Instant Poison on both, and he was using Shiv as his main attack! Revenger has a speed of 1.5, so Shiv costs only 35 energy, adds a combo point, and deals physical damage as well as the poison damage which is unmitigated by armor.

Here's an example of a Shiv spec:
http://www.wowhead.com/?talent=fhxboyZGMEz0Vzx0Got

This spec has the fast combo point generation of a Hemo spec, as well as a large amount of unmitigated damage from your poisons. With Combat Potency, every Shiv has a 20% chance to restore 15 energy. Over time (like on a boss fight) that's an average of 3 energy returned per Shiv, so in a way you could say it's only costing you 32 energy. That makes a HUGE difference.

There are 2 disadvantages to this spec. The first and most important is that it is HIGHLY dependant on itemization. Just like Hemo requires a really slow weapon to be viable, Shiv requires a really fast one. If you don't have a 1.5 speed or faster sword, fist, or mace to put in your off-hand, it's generally not worth it. (Why not a dagger? Remember that daggers are normalized so that all instant attacks with them count as if they were 1.7 speed, and all other one-handers are normalized at 2.4 speed.) The other disadvantage is poison immune mobs. Elementals (not plants, but the earth/air/fire/water ones) are often immune to poison, and that takes away a good chunk of your damage. You can Sinister Strike your way through these fights and still be okay.

ADVANTAGES:
High CP generation
Ridiculous energy regen
Unmitigated poison damage

DISADVANTAGES:
Highly dependant on itemization
DPS drops significantly on poison-immune mobs
Must always have poisons on hand and apply them often

Try it out, you just might like it. ^_^

May have missed it stated above, but I dont think its there.

Shiv can be used when you are main hand disarmed - this is extreemly useful in pvp against warriors or against certain bosses/mobs that can disarm you.

You can keep attacking and generate points whilst disarmed - very nice!