Thanks for all the information, Mark.

| A similar problem happened once before on a previous grml devel release. 
| (Don't you have any cheap external USB disks for testing?)

For sure, works without any problems here, so seems to be a problem with the 
kernel<->chipset.

I'll test the new grml ISO (providing 2.6.20-grml based on 2.6.20.11, will 
become the grml 1.0-rc1 release) with all the usb disks I can find, stay tuned.