I'm not really sure what to think about the Shadowy Apparition. On the one hand they're really cool and on the other hand they're actually really badly designed.
Right now, Shadowy Apparition is one among very few things that could get me to play shadowpriest. I'd love to have my own little Zinn run (or actually walk really slowly) to her demise. And seeing the shadowy apparitions of shadowpriest in the guild do this really cracks me up. I'm still thinking "What the heck is he doing? Doesn't he know standing there will kill... oh wait right, apparition!". I still haven't learned to distinguish them from the "real" thing and honestly there isn't much there to help me do that. Apart from the apparition behaving oddly, which isn't a good clue since most shadowpriests are pretty odd themselves, they look exactly the same as the Shadowpriest they came from. I'm far from the only one who's yelled "Watch out!" on ts because I thought some Shadowpriest was standing in a really bad place. Melfina over at WoWnoob has also found out what a pain these apparitions can be on fights like Putricide. Lethal actually.
I've got to hand it to Blizzard though, this is a really original skill. It can't be easy to come up with something that isn't like anything else already in the game by now. In a way one could say that the SA is just like those extra lightning bolts elemental shamans could proc, it's just shaped exactly like you instead. In a way it's a stroke of genious. Unfortunately it is also a good example of how really good ideas on paper don't always work out well when put to practice.
I've whined before about the fact that druids shapeshifts looking so alike created problems when raiding. Maybe I need to know where exactly one special boomkin or resto druid is, having to sift through a couple that looks exactly the same isn't exactly easy when I've got plenty of other things to think about. Fortunately that's not as much of an issue when it comes to resto druids anymore. And like I said then I really wished they would at least have given trees, and now boomkins, different kind of skins. Like bears and cats. It's bad enough that players basically look the same because they all wear the same endgame gear nowadays. If you have the two people playing the same class and race you can bet that telling them apart isn't going to be easy (unless they're hybrids). Blizzard then gives shadowpriests a skill that make the shadowpriest player vanish in a horde of shadowpriest apparitions. How could they not see that this was going to turn out be a problem?
Could be that Blizzard actually did foresee the issues, and have designed all Cataclysm content so that you don't ever have to tell people apart. But right now we do have to be able to tell people apart. We've got the abovementioned issue with sharing diseases on Putricide. If you can't tell if the person you're trying to give the disease to is real or not could have you dead very fast. Same thing with biting on Lady Deathwhisper. There are ways to get around these problems of course, but that forces people to change tactics they might've worked with for along time. Tactics that have worked perfectly well until now.
And even more oddly, you can target the Shadowy Apparitions, further creating annoying situations (fortunately enough your aoe heals don't heal them though, that would really set me nerdraging). There is no reason whatsoever to be able to target them since you can't affect them in any way. There are definitely a couple of things that need to be fixed here.
If only they could make the apparitions look less like the real deal the problem would be solved. Sure a little of the coolness of the spell will be gone, but these kind of compromises have to be done all the time. You can't have a spell just look extremely cool. It has also to be functional. I think Shadowy Apparition would be just as cool if they had some demon form, or whatnot, that looked nothing like the shadowpriest it came from. Blizzard, go fix!