I noticed that on my desktop machine (openSUSE 11.1 with KDE 4.2.0 from Factory), the Oxygen plasma theme has thick black borders (that look like they were drawn in MS Paint) around pop-up boxes, the KMenu, and KRunner whenever I disabled the KWin effects. If I choose the Aya theme, there's no border. However, on my laptop (same openSUSE 11.1 w KDE 4.2.0 from Factory) both plasma themes cause this black border. Since I don't always run the KWin effects, I find this very annoying. Has anyone else noticed this? Any clues on how to get rid of it?

This is because Plasma uses compositing for the nice rounded edges. When KWin effects are disabled, Plasma follows suit, and disables its compositing as well.

Hmm, interesting. However, all other plasma animations and effects are still running. Are they not using compositing?

I wonder why Plasma can't just keep simple clean lines without compositing? Most other non-compositing wms I've seen don't have ugly borders.

That'd be because the widgets have not been given opaque borders yet (atleast in your distro). Kubuntu gives me fairly nice opaque borders.

I don't see these thick borders when I have effects off. Looking at screenshots around the web, I'm not seeing them there either. It sounds like Plasma is trying to composite when compositing is off. I would log a bug on this (and include screenshot).