I found 0.8.2 to be extremely slow. Clicking a clip in project tree it takes about 3 seconds before the clip is actually selected. Using png-sequences, when selecting one in project tree the clip monitor shows a big red "Missing clip" although clip is shown on timeline and everything is right in clip properties.

Changing frame in timeline is also extremely slow, it takes about 10 seconds before project monitor updates.

I've tried all different settings I can think of, including chaning video driver, nothing seems to help.

what is going on!? Right now Kdenlive is in an unusanble state for me.

Does generating proxies for your png's help?

I've found 0.8.x slow in response to select and preview in the monitor windows, as you describe even with HD video clips, not as long delays as you describe but slow enough to notice especially when trying to edit at speed.

The missing clip problem I had with a certain revision from svn, but latest svn from sunabs PPA doesn't appear to have this problem.