Nicholas,
I too am am running the Imagemate (SDDR-31) USB -> CF adapter. It is great for development and debugging. Used it many times when porting linux to the Ipaq! My only frustration is that i am unable to boot of it. Once the kernel is loaded i can mount the CF card and make it the root filesystem, but that is about it.
If you really want to boot the USB->CF, you can use DOC with kexec as a boot loader. Then, you can mount the CF, and run kexec kernel from the CF.
-Andrew