Ubuntu 12.04 LTS uses, by default, Unity (3D), and Unity 2D as a fallback, useful and usable for users with low-specs computers, 2D session that provides a decent set of actions, enhancements and specific attributes.
It seems that, although Unity 2D is mainly to be "ignored" and the 3D session is to be usually chosen, there are Unity 2D-specific interactions that are highly anticipated or desired for the inclusion in Unity, like for instance the kinetic scrolling and the bounce effect, bundle of interactions that could/might add a more fluid, vivid scrolling in the Dash.
According to a bug on launchpad reported by Ubuntu's John Lea, the bounce effect is to land in Ubuntu 12.10's Unity 3D, "In Unity 2D, when a user attempts to scroll past the end of the Dash results, there is a kinetic 'bounce' effect. This needs to be ported to Unity 3D", "Implement the exact same kinetic 'bounce' effect that is used in Unity 2D in Unity 3D".
Probably, the bounce effect is to be "backed" by a new smooth scrolling, probably similar to Unity 2D's.