Exorte have you even read the other comments on shadowflame useage in pvp?
yes but most people think it is not good enough.
Mine REAl point is it has use, but the effect is not great.
Of cause every spell have it use( or why have them), it is just is it really good enough to spend the mana (and get close range in this case) to use it or not. (expect the old fire stone)
From a PvE point of view, i find it really handy on the Decontructor encounter when AoE'ing the ScrapBots.
Seed 'em all, then Shadowflame when they are in range - move on to next pack. It works far better then Hellfire as its an instant, dealing enough damage to pop SoC an leaves a small Dot. Sure SoC will procc itself but its not sufficient sometimes.
Leave Portal at your primary nuking position to port back asap.
Other than that there not really much use for an Affli specced WL.
When your in the middle of tactics and you wanna show the mage in the raid that your more ub3r than him. So you burp (shadow flame) in his face and to also show him that the spell sucks and so does his breath.
Although the spell is crap the animation is well cool
I believe the point here is that shadowflame offers virtually no utility.  A mage has cone of cold, blink (vastly superior to portal, btw), mana sheild, frost armor, etc... They don't have near the trouble with melee that a lock does.  This talent needs to be glyphed to even be relevant.  Beyond that, if you're facing a rogue you can assume you're snared, so snaring him = you're both snared and he still kicks your ass. So you have to hope that your in range of portal and its off CD...  Anyway, completely agree with the post, this spell need a huge boost before it even becomes relevant.
Well in PVE, other than in deconstructor adds; in theory it actually increases your dps if you use them in the right place in your rotation. BUT, not only do you have to use it next to the boss/enemy, but it costs almost double the mana of the rest of your regular rotation spells. So, in the end... no it has almost no use in pve.
Shadowflame, to me:
Glyphed - slow = win,
Regardless of glyph, Conflag = Daze = slow = win
Conflag'd = 2500 non crit, for me at least, which is around 10% of most peoples health, so nothing to sneeze at.
So basically people complain about our mobility in Destruction specs and then complain that our arsenel of instant, cast-while-moving spells suck.
Shadowflame + Conflag = enough room to cast fear or a DD spell or buy you enough time for your teleport.