So yeah - they have some uses, they're just not anywhere near as good as they way Blizzard made it sound they'd need to be.

It seems that in PVE especially they didn't bother balancing Soulburn among the specs. Most of the damage dealing spells attached to Soulburn are fire spells. As an affliction warlock, my talents don't boost anything I can use a Soul Shard on to a descent degree.
My Drain Life at it's current point is a 1.4 second channel after a Soulburn. It hits (according to Dr. Damage) for an average of 5829. With absolutely zero talents increasing the damage of Soul Fire it deals an average of 7115.

This means at no point during a boss fight should I not just use a destruction spell for damage. I used to use it for a little damage burst and a haste buff, but they took that away. The epic feel we were supposed to get from burning a soul isn't epic at all when I can use one every 45 seconds, three times a fight, and get a result weaker than my weakest Nightfall proc (my weakest Shadow Bolt is 7172), which happens more often than every 45 seconds. If I wanted to throw non-fel fireballs I would be a mage.

The only true affliction spell is Seed of Corruption. It refunds the shard, sure, but it's not worth the talent point to be useful in two raid fights I have seen so far.
We should be able to Soulburn Seed via a glyph, so we can take it out for the 80% of fights it is useless on.

I myself have never in PVE combat used a Soulburn on anything but Soul Fire or the occasional Drain Life just to help the healers out.

It would also be very nice if we got an extra spell that generated one soul shard and maybe did a minor amount of damage (roughly that of a Fel Flame). Instant cast. The catch is it would share CD with Soulburn. That way every 45 seconds we have to decide if we will need that soulburn CD or not. If not, fire off Soul Steal (that's what I named it), burn a GCD and trigger the Soulburn and Soul Steal CDs. Then we aren't limited to only 3 a fight, but aren't getting too many extra as it takes 1:30 for each new shard to be used. They can even just rework a current spell effect into pink and have it fire from the boss to the warlock when they cast it. A five minute fight would yield six casts of Soulburn/Soul Steal. That would be 2 extra Soulburns that currently allowed. That does not make us overpowered.

I know it would be asking for a lot more, and maybe too much, but I also think each spec's signature spell (Haunt, Hand of Gul'dan, Chaos Bolt) should have at least some sort of Soulburn effect. Those ones should be our big WOW spell. The one everyone in the raid knew we fired off.

I dunno about you, but when I hid SB:SoC that feels pretty awesome to me. Granted to be brutally honest thats one of the few places I feel it.

CORRUPTION. EVERYWHERE. AT ONCE.

I'll agree with this. Consider: even the most "exciting" Soul Burn - the instant cast Soul Fire - only turns a 3-second cast into a 1.5 second gcd. It nets you no more than one and a half seconds to use on your next spell. Handy? Sure, but bloody fire mages get the same thing as a routine proc.

There isn't really anything that cool with Soul Burn. I'll tell you what one should have been: Fel Flame, with the extension bumped up to 12 seconds, and having it work also on Corruption and the Bane DoTs. Would it be awesome? Yes, it would be. However, it'd also be the sort of thing which, while not amazing for raw dps, is amazing for dps-utility. As part of a regular rotation, it's probably not much more of a boost than Soul Burn, maybe 2 gcds in this case, but it would shine in special circumstances. Movement phases, target switches, just before an air phase begins, etc. Any time when you'd want your dots ticking, but wouldn't be able to keep them up normally. It wouldn't fix the offensive/defensive dual-use, but it would add some wow-factor.

Likewise, the Shadow Ward/Nether Ward transformation ought to have been a baseline Soul Burn effect for all locks.