I have a laptop with pretty "standard" hardware, intel core i5-460m with intel ironlake graphics and 4 gigs of ram. For the most part unity/compiz perform acceptably, but the dash is very noticeably laggy due to the active blur. Doing simple things like dragging an icon from the dash to the launcher is extremely laggy. In addition, on a cold boot the dash tags ~5 seconds just to open (so does the alt tab switcher). This is experienced in both 12.04 and the latest 12.10 beta.
For comparison, plasma's active blur effects in KDE 4.9 have absolutely no effect on my performance, and everything is always smooth. The dash really needs significant optimization work, as its slow and laggy on common hardware.
If I disable the blur things are fine, but the dash's heavy use of transparency makes this unusable (perhaps if blur is disabled the dash should be a darker color and more*opaque* similar to how it was in 11.04?).
Besides this issue unity performs reasonably well, but the dash is such a large part of the unity experience, that speed issues there really ruin everything.
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