This is a great thread, my USB key loads and mounts out of the box. I am still working on getting my MP3 player to mount properly and USB Ethernet dongle to show as a /dev/eth* net interface both kernel modules load and it appears they just need one or two more things to work. I just need to work my way up the thread a bit.
It would really help if those with successful fixes were posted or linked on the wiki. http://wiki.maemo.org/N900_Hardware_USB_Host