Yeah, DoTs stack in Skyrim with no limitations other than how fast you can apply them, from what I can tell. The tactic that revolves around using short bursts of Flames to rapidly stack the DoT has been around for a while, and more recently there's Ignite. I got it up to 57 damage per second with each stack (Augmented Flames 2/2 + Aspect of Terror + Ahzidal + Dual Cast). Pretty insane considering it's an Apprentice level spell.

It's a shame you can only lay one Rune at a time. Imagine layering 5 Poison Runes. Though I suppose if you could do that you might as well just layer 5 Fire/Frost/Lightning Runes and kill your target in one go.

I've been wondering on this, whether dual casting this rune just increases the duration of the poisoned effect or if it increases the DPS of it. also as soon as i have access to it im going to try it on draugr as they are not immune to ebony mail's poison-cloak effect.

It's too bad you cannot have a magic-using follower cast specific spells like runes. That way you can make a trap field like you find in certain dungeons of the Forsworn.

Interesting effect with the poison rune is that it stacks cumulatively, so if you have a crowd of units walk over dual casted poison runes several times, the DPS adds up quite quickly.

Deals 3 Damage in 30 Seconds.

Apparently, it's effected by fortify restoration. Imagine a fortify restoration armor set. That could literally make the poison rune the spell with the highest damage output in the game. Great for assassin mages.