In case some people read the older posts about this spell not being mana efficient and not worth getting, dont listen to them.
Necro and Shaman curse lines are great for DPS and were not designed for DPM, if for example you have a healing mob your barely able to take, this is a perfect use for this spell, just pile it on with your other dots, then blast away- you may just be able to out damage its self healing. the healing type stormriders in bot are a perfect example of this type of mob.
Also, i would just like to add that with the new combat cooldown system, the old models of mana efficiency are somewhat redundant and in a lot of cases it is now more efficient for kills per hour to blast till OOM then med to full, which is very different to the old style of, drop your best DPM DoTs and med thru the fight to perma chain mobs. thus making these curse spells far more usefull for standard kills.
Just my 2cents