Can't create kext cache under / - owner not root
An hour later...

Well that's interesting: if I stick it into a different device (a little usb camera) and plug that in, it complains a bit, then mounts!?

Mar 26 18:37:34 Johns-iMac.local com.apple.kextd[19]: Can't create kext cache under / - owner not root.
Mar 26 18:37:34 Johns-iMac.local com.apple.kextd[19]: IOBluetoothHostControllerUARTTransport.kext has no Info.plist file.
Mar 26 18:37:34 Johns-iMac.local com.apple.kextd[19]: Can't create kext cache under / - owner not root.
Mar 26 18:37:34 --- last message repeated 2 times ---
Mar 26 18:37:34 Johns-iMac kernel[0]: USBMSC Identifier (non-unique): 966110000000100 0x603 0x1001 0x100, 2
Mar 26 18:37:36 Johns-iMac.local com.apple.kextd[19]: Can't create kext cache under / - owner not root.
Mar 26 18:37:36 Johns-iMac.local com.apple.kextd[19]: IOBluetoothHostControllerUARTTransport.kext has no Info.plist file.
Mar 26 18:37:36 Johns-iMac.local com.apple.kextd[19]: Can't create kext cache under / - owner not root.
Mar 26 18:37:36 --- last message repeated 2 times ---
Mar 26 18:37:36 Johns-iMac.local fseventsd[20]: check_vol_last_mod_time:XXX failed to get mount time (25; &amp;mount_time == 0x101eff498)
Mar 26 18:37:36 Johns-iMac.local fseventsd[20]: log dir: /Volumes/xbianboot/.fseventsd getting new uuid: 4898DEB3-E8EE-4FB0-BD08-EBECC37F3872
Mar 26 18:37:36 Johns-iMac.local mds[32]: (Volume.Normal:2464) volume:0x7f9020906800 ********** Bootstrapped Creating a default store:1 SpotLoc:(null) SpotVerLoc:(null) occlude:0 /Volumes/xbianboot


From there Disk Utility is able to see it and I can Erase the contents and start over.

Came down to not using the usb multi card reader thingy.