"If you force yet another custom, badly-implemented, weirdly-behaving, not-entirely-thought-through scrollbar on me, I will hate you and never visit your website again."

Pretty sure Gmail uses custom scrollbars and I wouldn't be surprised if it's the most commonly used e-mail in the world.

I think Facebook also uses a custom scrollbar on their activity feed.

Same with Rdio's web app and Spotify's web app (unless it looks different on PC?)