research - Do people use `jump to top of page` links?

I'm talking about links or buttons at the bottom of the page or screen simply linking to the top of the website.

Is there any data on that?
Are they used more frequently on long pages?
What about mobile?

I know that iOS has a built in function for it, but I don't know if people actually know this and I also don't know if it works on Android and WP7.