No, I haven't gone completely samurai. It is a lot cooler than a sweaty feather pillow in these stifflingly humid summer nights.
These things are sold in Japan as "summer pillows" and they work. They seem to be made of a similar sort of woven staw as tatami mats. They are harder than a normal pillow but quite quishy, with some kind of bunched up straw or plastic inside. Thanks to this one, I got some sleep last night.