I find it extremely distracting. A little hard to describe, but it is sort of like trying to remember one number while someone is babbling other numbers, or trying to keep a train of thought while listening to multiple other conversations.
There's also the visual noise - I hate it for the same reason I hate tool tips and similar. Popping up flyovers on top of whatever I'm trying to focus on is utterly infuriating and I've never understood why people think that's good UI. It is like shoving your hand in my face if I look at you.
A lot of autocomplete systems will put text into the document FOR you, like when you press enter or space or something. It is infuriating. Having the suggestions that you can access if you want is usually fine, but sometimes also having that bubble pop up and cover code below or above that you need to see is also infuriating.
There's also the visual noise - I hate it for the same reason I hate tool tips and similar. Popping up flyovers on top of whatever I'm trying to focus on is utterly infuriating and I've never understood why people think that's good UI. It is like shoving your hand in my face if I look at you.