http://askubuntu.com/questions/134346/why-is-unity-2d-being-discontinued And just when I was getting to know you.
meh! i found the last Ubuntu sluggish on my 5 years old computer. hopefully, it works much better on newer machines. this last move will make it even harder for people with older machines.
Unity 3D is snappy for me on a 2009 Dell 1545 laptop. But then I don't compare FPS or whatever. In other words, no heavy graphics. My formula- and macro-heavy spreadsheets open quickly in Calc. Even editing spreadsheets in Google Docs is a joy. I was trying out 2D to see if I could notice it being "lighter". Can't say I notice much. It's back to 3D tomorrow.
They are discontinuing unity-2d as a separate project. 2d support is planned be integrated with what is currently unity-3d.
On the one hand, this doesn't sound so great for users of low-spec computers. On the other hand, Unity 2D is itself pretty sluggish, and really only pays lip service to the idea of running Ubuntu on low-spec computers. (FWIW: 12.04 with Unity 2D is slow as molasses on a Core 2 Duo workstation with 4 GB of RAM, which is not by any means what I'd call low-spec. The bloat is totally out of control.) I'm really a bit disturbed by the way major desktop distros (and desktop environment projects) are abandoning all pretense of running on low-powered hardware. Maybe I'm being sentimental... But one of the big reasons I migrated to Linux in the first place was that it could run - not badly, either - on a Pentium II desktop with 192 MB of RAM. And through most of high school I was using a Powerspec desktop with 128 MB of RAM, which Linux also ran quite well on. Expecting anything to run with less than 256 MB would be a bit much these days, but I'm still quite disappointed to see this OS getting so porcine that it can't run properly with 4 GB and a Core 2 Duo. It strikes me as bending quite unnecessarily to the industry's desire for planned hardware obsolescence.
Both Unity 2 and 3D run quite snappily on my HP 2.0 ghz laptop with 4 gigs of ram. It does have an nvidia video card in it, though. I guess it depends upon your hardware as to how well Unity runs. Later...
i found moving a windows fastly around was not as smooth as i'd like. of course, i can't complain because i'm using a 5 years old computer. but the graphic responsiveness is much better with Bodhi Linux, or Windows 7.