Along with just entering the URL you want to highlight you also have the option of installing the awesome highlighter firefox extension. If you register for an account all of your highlighted pages are stored in your account for future reference.

I made a very short demo of the system.

After talking to the sites founders I got some insight into where the idea for the website came from.

We were working in a shipping yard and there was an accident. A box of
bricks fell, nearly crushing us…but a highlighter swooped in to save us.
From that day forward, we swore to promote the idea of highlighting and
sharing text to the world.

Pretty crazy.

It’s a really simple idea that’s been executed really well. It’s definitely a service I will be using often.