Just wanted to comment a bit, now that I've finally ran a bunch of instances after 75+ levels (yeah, it's better you don't ask why its taken so long).
I've been able to run a whopping two runs out of 10 or so as Shadow/DPS. There were like 2 or 3 that I was invited to come as DPS, but in the end wound up healing (because the guy who said "I can heal!" did kind of a crappy job on his own). In the two I've DPS'd my output has been... bleh. I did Gundrak the other night with DK/SPriest/SPriest(me)/DiscPriest/and I think a Mage. Aside from the fact it was one of the smoothest PUG's I've done (although last night's UK PUG wins hands down- tied with my first flawless attempt at Nexus), my damage was lacking. A lot. And the worst part was, the other SPriest was *3* levels lower than me (73vs.76), and had respecced right before we went in into Shadow (he didn't even have all his talents set on the first few bunches of mobs). He had a bunch of t6 gear though, compared to my mimshmosh of tailored stuff+Quest Rewards... that's the only difference I can think of. Oh, and all he did was spam Mind Flay. Mind Flay Mind Flay Mind Flay.
I had somewhat of a rotation: VT>VE>DP>SW:D>MB>SW:P>MF, I'd MF until replenishment dropped, then (assuming I had time- usually on bosses) recast VT+MB to put it back up. If I moved too far on the hate list, I'd toss a Fade and drop my threat back down. I felt like I was pulling my weight... but still got outclassed badly. :(
My armory is here: http://www.wowarmory.com/character-sheet.xml?r=Ner%27zhul&n=Binya I have some extra +hit stuff I can swap in, dunno if that makes that much of a difference (it does drop my Spell Power a bit though). My talents are pretty standard as far as Shadow goes, I think. Meh, it's just bothering me.
On the other end, I've healed a whole bunch of stuff, and sort of have a quasi make-shift healing set (it's mostly MP5 gear and some extra Spirit stuff). I started eating MP5 food as well (Pickled Fangtooth ftw), and as long as everyone in the group is halfway competent, I pretty much have very little issues (I do love DK tanks now though. Good ones, anyway :3).
I have noticed that life would be SO MUCH easier of I were Disc/Holy or vice-versa. However, I've definitely come from my solo-only, don't want responsibility of other people's lives mindset I used to have to *gasp* enjoy healing again. I'm pretty sure once I hit 80 I'm respeccing until dual specs are released (hopefully in this lifetime), since 9 times out of 10 I'm called on to heal rather than DPS anyway.
But I'm rambling.
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tl;dr version:
Got to DPS as Shadow a couple times and had crappy damage output vs. an SPriest 3 levels under me. Had to heal a ton of times now and am finally getting the hang of it and learning to enjoy it again. Dual Specs need to come soon and make my life easier though. :3
One quick question- I have 3 pretty sexy weapons in my posession. I'm currently using the one with the highest amount of Spellpower, but which of these would you use and why (the other two are sitting in my bank now... I need some room, haha).
Tower of the Infinite Mind vs. Staff of the Great Reptile vs. Frozen Scepter of Necromancy + Suntouched Flowers