How to create Google Wave-like scrollbars?

It is a custom element ( maybe a div ) that acts like a scroll bar.

You can find a number of implementation using jQuery

jScrollPane

Here http://jebaird.com/blog/shortscroll-jquery-ui-google-wave-style-scroll-bar, it is similar but has not all Google Wave functionality.

This should get you pretty close: http://konrness.com/javascript/google-wave-style-scroll-bar-jquery-plugin/