My assumption is yes, but I've yet to figure out in game how to check this hypothesis. So, in the absence of finding proof on my own, I come to you - the Skyrim masses - for this answer. I.e., Gloves w. 30% Alchemy Bonus + Armor w. 20% Alchemy Bonus = 50% Alchemy Bonus?

Yes, they stack.

Oh yes.

Yay for looping!

They do, but potions of varying magnitudes no longer stack. Someone correct me if I'm wrong.

To my knowledge, potions never stacked. Only the last consumed was in effect.