first of all: my answer isn't based on facts or numbers. its just my way to play and my experience.
if you have adds that will move along a predestinated way, you shouldn't have any problems. just predict the position of the adds in 3 GCDs (~3sec), plant your shrooms there and detonate afterwards. the second set of shrooms is a little more tricky but nothing really hard. since your detonation should be on cooldown you have to predict the adds place when your detonation comes off cooldown.
on fights like maloriak HC its really hard to play as a moonkin, BUT if you do it right you can do some nasty DPS.
there are several things u can do to ease your life.
1. mark the addtank with a clearly visible mark. since i have nameplates activated (for doting, and i think everybody should see nameplates, always!) those nameplates jump around like hell and prevent a good view on the tank and the adds...
2. talk to your addtank BEFORE the pull and IN the fight. since our tank is kiting the adds counterclockwise, i put up my first 3 shrooms (ofcourse before the pull) 10-20yards left of maloriak. our tank gathers the adds infront of maloriak (here i dot them, see below) and when he thinks he's got enough aggro, he'll pull them to my shrooms and begins his kiting circuit. on this ciruit i try to plant my shrooms ~20yards in front of him and tell him were i planted them.
the whole difficulty is to get as near as possible to using detonation on CD, while dot up as many adds as possible. sounds easy, but is very hard to manage if you factor in SS procs, starfall, typhoon, jumping nameplates and those nasty voids. and even harder if you try to hit high-hp-adds first with dots and SS procs. or if you try to get the best use of your 4p-t11-bonus (detonate shrooms while active, DONT activate starfall while active)
3. help your tank. put thorns on him when all adds have been spawned. have a rogue and/or hunter help the tanks aggro.
of couse use an aoe tanking class. in my experience palys did best. these hints are even more important if you take the 4th hint.
4. with my level of haste its working very very fine to start with lunareclipse, so i reach solareclipse right when the adds spawn. (since patch 4.0.6 you can decide which way to go at the beginning). so the start looks like that: treants, starfall, dots, wrath, starsurge, wrath till lunar. normal rotation till solar.
if i get solar before the adds spawn, i will continue casting starfire and will NOT refresh my dots, but in most situations i will get into solar when the first 1-3 adds already spawned. gives the tank some time for gathering them...
in the moment i get solar: typhoon, (starfall if rdy again, ok.. needs some procluck
), pop berserk (yeah troll rulz!!), dot up the adds and detonate shrooms (if the tank is already next to them).
the dots will do alot of dmg/aggro (berserk + NG), typhon will add some aggro, starfall might add some aggro and especially those shrooms aggro like hell........................
thats why point 3 is so important.
for sure shrooms are not the easiest way for aoe-dmg (Smurf those hellfirespamming warlocks!
) and its taking some time to get used to it, but its absolutly viable and i like to be a skill-need-class.
i hope i was able to help you.
PS: to my fellow theorycrafters: is there a min-number of targets for the shrooms to be viable?