The CN-301 USB SmartMedia adaptor from Sitecom can be used under Linux with a little fiddling.
You will need a kernel that includes Simon Munton's patch to support the SanDisk SDDR-55. This is included in the mainstream kernel distribution since 2.4.20. Note that you need to enable this support under "USB Mass Storage support" in the kernel configuration.
The CN-301 appears to be the same type of device, although it appears with vendor/product ID 0x0c0b/0xa103, which identifies the original manufacturer as "Dura Micro, Inc. (Acomdata)". Sure enough, Acomdata have an identical looking device, the MF1SM. I assume that this is the same device with different badging and will thus work identically, although I only have the CN-301 available to test.
The following small patch to Linux 2.4.21 will enable the usb-storage driver to recognise and use both devices:
linux-2.4.21-acomdata-mf1sm.diff
To apply the patch, execute the following command in your Linux source directory:
$ patch -p0 < filename
where filename is the location of the downloaded diff file.