If multiple items have the same enchantment, does the bonus stack?
Certain enchantments can be applied to multiple items, such as both an amulet and a ring. If I wear two items that grant the same bonus, does the bonus stack? (e.g. if I wear an amulet of +12% Alchemy and a ring of +12% Alchemy, do I get +24% to Alchemy?)
Also, do some enchantments stack while others don't?
Instances of Fortify X (Where X is "Conjuration, Smithing, One-handed, etc.") stack if they're from separate items.
You cannot use the "Double Enchantment" perk in the enchanting tree to double-enchant a single item with the same enchantment, twice.
Unlike in Oblivion, stacking skills above 100 actually increases their effectiveness.
Well, it *should* increase their effectiveness. However, there's evidence that this is bugged, at the very least for Pickpocketing, and possibly for Enchanting and Smithing as well under some circumstances.
I tested this with multiple items of Fortify Smithing, and confirmed that it works. Adding the second item allowed a weapon to be upgraded further than one item. Do non-skill enhancements stack (e.g. Fortify Carry Weight, Fortify Health, Fortify Magicka Regen, Resist Magic)?