Whenever I try to enter CSS it's always really, really slow. I type a property, and then I have to wait at least 1-2 seconds for it to appear in the editor; it usually appears in sections, a few letters at a time. For comparison, this does not happen when using the Webkit Web Inspector instead of the new Web Inspector (Webkit Nightly), or on the Safari 6 inspector. While the CSS still works, it's almost unusable as a lot of the time the letters come out in the wrong order. I am on Webkit r148272.
I confirm that, still slow on june 12 build.
This was fixed a while ago. But it sounds like we have another issue in newer builds.