I came close tonight... the SanDisk MicroMate SDHC reader. It *almost* works. I can set the N810 to host mode (my USB key won't do that) and it gives me the standard unsupported device message. I used the microSDHC card I had in the device inside the reader so I knew it was good. However, the nokia complained about the card not having a file system. (it's VFAT).

My *guess* is that the LED indicator light on the device is a reasonable indicator that it draws too much power. My USB key has a big blue light.

I'm going to try a few cheaper USB key types and see if I can find one that lacks that feature. All I need is a 4GB key that can hold a few hours of transcoded movies and music.