In the fancy new GDNet chat, it doesn't scroll to the bottom every time someone posts a message (which is rather annoying). I make sure I scroll all the way to the bottom of the chat window, but every time a new message is sent the window doesn't auto scroll down. Here's a before and after picture:
Before (all the way scrolled to the bottom):
After someone sends a message:
OS X 10.8.4
MacBook Pro Retina 15"