I don't know how the things work on the Fire, but in the ad supported e-ink kindles the ads are fairly unobtrusive. They appear on the rotating "screensaver" images (so you see them when you first pick up and start to use the device) and also as a banner on the home screen. They don't appear when you're reading books or otherwise using your Kindle. The ads I've seen were pretty tasteful too. No "one weird trick" belly fat ads or stuff like that.

I only had a Kindle Touch for a brief time but I seem to remember that there were some ads that I thought were not so great for kids. The kindle would just lie around in the flat, so kids would get their hands on it, too. Not so great in that they featured some mildly erotic or violent images (I don't remember exactly unfortunately - it certainly wasn't that big a concern, but it is worrying since you can not control what images will appear).

Because someone of us are sick of seeing ads. (Kindle owner but mine isn't ad supported).

The banner on the home screen is pretty annoying.

I barely notice it, especially since, reading books, I rarely visit the home screen.