Title says it all.
A floating button which allows users to go to the top of the page at any point could always come handy.
Especially in threads with huge pictures or long texts.

Why can't they just click the top of the scroll bar?

It's much faster and easier to navigate to the top of the page with the button I'm talking about than using the scroll bar.
And also, just like Jeffry36 said, it could come so handy for mobile users.

Some people might be on a mobile device and cant scroll. As i am right now. I for one am all for this idea cus i get tired of needing to slide up all the time. I also like the design you made for it, really simple

Mobile wise, this would be handy.
Computer wise, useless imo.
That's my thought of it.

Not everyone might find it useful.
Because, most of the users are used to use the scroll bar.
This feature is so handy in websites like tumblr as far as there are long and big pages.
And so that some threads at toribash forum are long, this button can be found useful sometimes.

Show yourself, I would (since I am using opera) zoom out and then scroll up.

I think it would be fine for mobil as everyone else is saying, on the site just scroll up?