I'm really getting tired of people spreading misinformation about enchantments on this forum. I've heard numerous people state that magicka regen bonuses don't work in combat, and I decided to test it out for myself. I initiated combat with a wolf, used a few spells to drain my magicka, and let it recharge without wearing any regen gear. It recovered very slowly. I then equipped my Archmage Robes, a custom necklace and Morokei for plus 250% regen, and sure enough, my magicka began to regenerate much faster.
I think people are getting confused because Magicka regenerates slower in combat overall. The same goes for Stamina. Seriously, test it out for yourself. The regen bonuses are vital for continuous spellcasting in combat.