The window button in the panel of an application that needs attention (like xchat with a new query message) stops flashing after a few times. In 4.6 it would flash forever so you couldn't miss it.
Fixed in ccd8488.
Well.... I like the gnome2-way. Flash for some time but show the entry highlighted after stop blinking. It's annoying for chatting if it pushes you to click on that window. Is it possible to create an option for it? A hidden one would be enough....
Added a feature request for this in bug #7746.