I've consistently always needed to stick to older computers at home. I've tried both 'Unity2D' and '3D' on my present computer (Toshiba Satellite, ATI Mobility 4200 series GPU, can post lshw if it's critical to do so) and I've noted that 3D mode is a notable performance hit, to pretty much every aspect of the computer.

Ubuntu 13.04 is being lauded as being quite fast - but 'Unity2D' is being dropped, is it not? Do the performance increases which most people seem to be experiencing require Unity3D?

Before people recommend other desktops - I've tried them and I just don't care for them I'm afraid. I really like the Unity desktop, and while I guess I could adapt to something else I just strongly prefer this UX to the others, so before telling me to switch DEs I'd like to understand a little more about the nature of the performance improvements.