I've noticed this for a while, but only now has it been so bad that I'm able to pinpoint the issue. A while back, I noticed that if I used my iPhone 5 while charging and my MBP while charging, the MBP would feel sort of tingly. Last night, I had my MBP in my lap with one hand on it and I went to select some music for my alarm on my iPod on my iHome and I noticed the iPod felt tingly as well. Today, I decided to investigate and I notice that my MBP feel tingly if I use it with anything that is not grounded (my iPhone charger, my iHome). Keep in mind, I'm using an 85w MagSafe charger with my 15" MBP with the extension (grounded) plug. I have it connected to a powerstrip that tells me if it's grounded or not. I know its ground detection feature works because I used to use it with an adapter for it to work in a non grounded plug and the not grounded light was on. Now that I'm using a grounded plug, the not grounded light is off. So my MBP is (as far as I can tell) grounded, but my iPhone and iHome are not. Is there something wrong with my MBP? Something wrong with the magsafe? Any further steps to troubleshoot? As my signature states, I have another MBP which also happens to exhibit the issue. I have another magsafe adapter which I can test if needed. Keep in mind that I'm very familiar with the internal components of it, and if needed, I can check if a grounding pin or something is missing (I bought the MBP used). ---------- Alright I tested my second magsafe charger and it exhibits the same issue if and only if I use the same grounded extension cord (original Apple, slides into the power brick). If I use the non grounded "duckhead," it does NOT exhibit the issue. It seems that everything is isolated and should not be, so when I am touching something grounded (my MBP), I serve as the middle piece (electrolyte?) to ground the isolated electrical devices. If I hold one hand on my MBP, lick a finger on my other hand, and touch my iPod or a metal part of my iHome, it's a pretty nice shock.