Major glitch with the Idiot Savant perk. For those who don't know, Idiot Savant is a perk in the Luck tree which has a chance to multiply the experience you get from any action by 3 at level 1, 5 at level two. The chance for this to occur has an inverse relationship with your intelligence, to a maximum of 11% at 1 Intelligence. At level 3 of this perk, it also has the added effect of causing all experience you get from killing enemies to be multiplied by 3 for a certain amount of time after the perk triggers.

HOWEVER, the level 3 perk is currently bugged, and no longer grants the benefits from the level 2 version for numerous types of trigger, most notably for quest experience. Previously, level 2 Idiot Savant was a great way to level up quickly, by saving just before completing a quest, and reloading the save again and again until the perk triggered, thus multiplying all quest experience received by 5. However, once you select the level 3 version of the perk, it will no longer multiply quest experience. It will still trigger, and make the funny little Vault-Boy animation and sound, but the experience received for the quest will be the exact same as if the perk had not triggered at all.

Please Bethesda, any bug that makes a perk significantly worse after being upgraded, making the user wish terribly that they had not upgraded the perk in the first place and cry out for a re-spec option, is a pretty serious bug. In the meantime, I hope others will see this and not make the same mistake I did.

TL;DR: DO NOT LEVEL UP IDIOT SAVANT TO LEVEL 3 UNTIL THIS BUG IS FIXED

After a bit more testing, I'm pretty sure the perk doesn't multiply any experience for any trigger anymore, except the x3 experience for kills after a trigger. Which means funnily enough, it doesn't multiply the experience of the first kill you get which triggers it, but it does for the next few you get in the next few seconds. Please Bethesda, this is a serious bug which practically ruined my character's build. I so wish I had known about this bug before I selected the level 3 version of this perk.