Ah, Feign Death. Every hunter's best friend. (And if it's not your best friend, you should go give it a /hug and make up with it right now.)
When I was a wee baby hunterling and I first got Feign Death, I was super excited. "OMG yay! Now all those times when I'm dying, I can escape!"
Now, is that a use for Feign Death? Yup. But is that the extent of Feign Death's potential? Oh no, it's not even scratching the surface. I have three hunters now that are a high enough level to know Feign Death, and with each one it's a very happy day when I train it, and with each one the first thing I do is try it out.
Now I know a lot of people are hyped up about Wrath of the Lich King, but until then there are still a lot of hunters out there that need Kindergarten (I see 'em all the time), so let's talk about Feign Death.
When You Should Use Feign Death:
1.) In an instance/raid situation to avoid grabbing aggro from the tank (or your pet, when soloing). This is crucial and at endgame, this is probably when you will be using Feign Death the most. It is vital to get a threat meter and watch your threat. It is also vital to get a feel for gauging your threat without the meter because sometimes it lies. (True story: Omen once told me I was at about 60-70% of the tank's threat on Prince, which I thought gave me plenty of buffer room. Prince disagreed. Raid wiped. Lesson learned.)
Now, the point is to Feign BEFORE you nab aggro. If so, you will be successfully cleared from the threat list and you will be able to unleash the Dee Pee Ess.
And if it resists? Then what?
Then you stop DPS.
Yes, hunter, I just told you to stop DPS. Hit the brakes, slow down, COMPLETELY stop shooting if you have to. Your numbers on the damage meter are not worth the repair bills and wasted time of a potential wipe. It shouldn't take too long for the tank to surpass you by a decent margin again, and once he does, Misdirect onto him. Your Feign Death should be up again before you have to stop DPS again.
2.) If you have already grabbed aggro... So Omen decided to be a poopyhead or maybe you just plain weren't paying attention, or maybe the tank got feared or something like that. Now what you should do here largely depends on the situation (is a wipe incoming, is the tank gone, etc.) but in most cases you will want to run to the tank-- so he can easily snatch aggro back up-- and then Feign. Do not Feign right next to the healer/mage/lock. They will give you dirty looks for the rest of the night and possibly hurl soul shards at you, and those things are pointy.
3.) When things go wrong... What if something horrible happened, the tank dies mid-pull in some Heroic and the mob lunges at you? Well here's where you make a choice and decide if you still have a chance or not. If we've got most everything decently CC'd and a good healer, I'll usually sic my pet on the mob, turn on Growl, pop Intimidation and Mend Pet, and yell out "ALL HEALS ON PET" over Vent. This can work quite well (but seriously, if you're in a Heroic, you will need a good healer for it).
What if people are dying left and right and it's down to you and the squishies? Wellll, things often get a little hazy around here, with different people having different opinions, but I'll tell you what I do. I dunno about you guys, but personally, I feel uncomfortable about having to watch a mob eat the priest while I lay cozily nearby all Feign Death'ed and safe. So even if a wipe is incoming I give it my all anyway, in a last ditch effort to pull off some hunter trick or other, and I don't Feign until the last second. Sometimes I get too daring and the mob ends up waltzing over and handing my butt to me before I can Feign, but hey, I kinda like it that way. I don't go down without a fight. And I've seen some epic stuff happen that way:
Your mileage may vary!
4.) To escape mobs: Often, when you are out in the field, you'll get ambushed by a bunch of mobs and you don't feel like fighting them at the moment. Feign Death works wonders. "But Pike, then they all attack my poor pet!" I know. But if you mount up really quickly after you stop Feigning and skedaddle, you and your pet get away scot-free. Pro tip: If you use Arikara the mobs will get bored and run away right before he makes his flashy entrance and you won't have to worry about it. (Off-topic, but WTB Petopia search for my Firefox Search Bar, PST.)
5.) In PvP: Most people don't fall for your Feign in PvP, but some do. Myself, I use it on hunter/warlock/etc. pets. They send your pet at you, you Feign, their pet runs away, and 95% of the time they fail to send it back after you. (I have often said that I hardly ever lose to other hunters in one-on-one PvP unless they are over 5 levels higher than me. This is one of the big reasons why.* Shhh, I'm trusting you with my secret!) Also useful against the NPCs in AV.
6.) As a party trick: I love going into the middle of some random holiday celebration in Stormwind, having my poor character drink herself into oblivion, then make some sort of statement about not feeling good and... bam! Hit the ground. I dunno, maybe it's just me, but I think it's hilarious.
Well, I hope I have managed to provide a satisfactory run-down of Feign Death and its usefulness. BRK recently wrote up a very good list of tips for WoW bloggers, and one of those tips was "don't worry about your niche". That's nice to know, because it's hard to find a niche as a Beast Master Hunter Blogger with the Jedi Master himself looking over your shoulder, but at the same time, I'd like to think I have managed to make my own niche by providing step-by-step and easy-to-understand guides for newer hunters or newer WoWers. I am always looking for ways to improve though, so as always, leave me your feedback!
* Second biggest reason: they sit there and spend approximately a million and a half years trying to pop off an Aimed Shot while my pet and my instant-cast shots nip hungrily at their cast bar.