Update: Though it's not fully clear to me why this Q should be off-topic and I have doubts that a bug report will help, I filed a bug report at https://bugs.launchpad.net/unity/+bug/1067349 Please vote for it if you are affected, too!
I have a nice Lenovo Thinkpad Edge 11 AMD Neo II with a ATI Radeon 4225 integrated graphics device. In my perception this is already a not-so-lowspeced device, but still a netbook.
Up to Ubuntu 12.04 precise pangolin I preferred Unity2D over Unity mainly because it did perform much better than Unity and moreover I was able to achieve 5-6h with one battery charge. The typical load of an idling desktop settled around 0.00 to 0.02.
Yesterday I tried the new Beta 2 of Ubuntu Quantal Quetzal: This does no longer offer a Unity2D version. The performance itself has definitely improved over Unity in precise, but nevertheless I do experience now a minimum load of 0.24 to 0.36 while completely idling. According to top this is mainly due to compiz eating about 3-6% CPU all the time.
In comparison to my Unity2D experience, quantal is more sluggish, eats much faster my battery and produces significant more fan noise. I already tried a few tweaks like static blurring, fast texture renderer or choosing alternate window manager.
Are there ways which enable me to continue to use Ubuntu/Unity on my device without major loss of functionality, performance and battery life?