Yeah, I can confirm that I generally am having really good signal strength, yet it lags. All possible interference is FAR from even the other side of the MBP. I think it's a driver issue when it comes to Magic Mouse. I have 2 and both do the same thing. It MAY be a problem with the firmware in the actual mouse itself, but no way of knowing. It's quite annoying. I had the problem on my old bluetooth chip, then I upgraded the chip so I could have hand-off, but this chip does it too. No, disabling wifi, or Bluetooth PAN, or hand-off, or changing (brand-new) batteries, or new mousepad (actually, that sometimes DID help, but that's for other reasons), or jumping up and down and twirling your tongue around your nose, or SMC reset, or PRAM reset DO NOT WORK! It's a software issue. "SmoothMouse" seems to help slightly, but it just creates a really fast laggy cursor. I've also read that this happens with Logitech mice, and in my experience, even having it right up next to the laptop has also resulted in the same problems. Additionally, the keyboard does have some issues (occasionally) with laggy typing, but again, I'm not convinced that it's a signal strength error. MAYBE interference with wifi, but still have the same problem when wifi is off. MAYBE hard drives, but I have this problem even when I'm at my coffee table.
You should be able to use a keyboard tray that slides under your desk and have the bluetooth be fine. You should also be able to use a laptop riser. These are basic things that just make sense, given the money we pay. (I paid $3,500 for my laptop back in 2011). This is ridiculous. Less than 2 feet away, nothing at all should cause any signal degradation, much less a wooden desk. Also, I use MacID to auto-lock my macbook pro when I walk away (yes, I've even disabled that and no it doesn't solve it) and I can tell that the mac bluetooth chip screws up even with that, because it often says "about to lock computer, due to proximity). SO yes, maybe interference, but I don't think it's necessarily just that.
