said by Goldheart:
Ah right, Dark Soul: Instability does increase crit chance by 30% for 20 seconds.
The glyph of Dark Soul has a passive bonus of 3% to crit (except on cooldown) but at the cost of only 20% bonus. Could be useful.
This might be implied, but to be specific ...
The glyph is only good if you expect Dark Soul to be off cooldown due to sandbagging for higher damage phases or some such. Otherwise, it should generally be on CD constantly, so it ends up being a pure nerf.
That said, I use it for questing because I'm not usually blowing DS to kill 3 mobs.