So, I have a mixed party (Pally, Priest, 2xMage, 1xWarlock) and I usually handle AoE 2 ways - the mages cast Blizzard, while the Warlock casts Rain of Fire (using Octopus to broadcast so they are all going at the same time) or I have the Mages cast AE, while the priest had a macro to cast Holy Nova every 4th cast (so my priest wouldn't go OOM). The problem was, I didn't want the Warlock to Hellfire in that situation because ... Hellfire is a really stupid spell in the end. If the lock gets aggro at all... dead lock. So, I played around with the idea of the warlock casting the only other "non-mouse" AoE spell they have - Seed of Corruption. While casting this on my tank's target is cool, it really doesn't do much there. Additionally, using a /targetenemy seemed like a bad idea because what happens if my warlock grabs a whole new group on accident? So, I came up with this macro and must say that I am very happy with it. With all of my toons spamming as fast as they can, as long as there are 3 or more mobs my warlock will out damage the mages every time... with just this one macro.

#showtooltip Seed of Corruption
/console targetNearestDistance 10.000000
/targetenemy
/console targetNearestDistance 41.000000
/cast Seed of Corruption

I would not use it for normal casting of the spell - I just have it mapped to the same key I have for the AoE. The sight distance is perfect because I won't ever grab mobs that wouldn't already be in combat. The best part is that it doesn't even really tick - since the 2 AE's that happen from the mages are enough to set it off - so even if the lock bounces back and forth between 2 targets ... I do the same amount of damage

Just thought I'd share, and happy hunting