Comment 2 for bug 1278131

It is Gala indeed:
http://bazaar.launchpad.net/~gala-dev/gala/trunk/view/head:/src/Plugin.vala#L643

It seems like it would be fairly easy to change the animation, but tricky to only animate when entering the menu bar.
I think setting the gravity to North would look nicer for dropdown menus, but maybe popups look nicer as they are now.