Factory-configured DreamPlugs need their internal u-boot firmware updated and
re-configured to boot from the SD card. 

You may want to remove the internal microSD card for the sake of simplicity.
This will result in u-boot and linux boot warnings, but these can be ignored.

The desired u-boot configuration is: 

    baudrate=115200
    bootargs=console=ttyS0,115200 root=/dev/sdb2 rootdelay=10
    bootcmd=${x_bootcmd_usb}; ${x_bootcmd_kernel}; ${x_bootcmd_initrd}; setenv bootargs ${x_bootargs} ${x_bootargs_root}; bootm 0x6400000 0x6900000;
    x_bootargs=console=ttyS0,115200
    x_bootargs_root=root=/dev/sdb2 rootdelay=10
    x_bootcmd_initrd=fatload usb 1:1 0x6900000 uInitrd
    x_bootcmd_kernel=fatload usb 1:1 0x6400000 uImage
    x_bootcmd_usb=usb start

HOWTO: flash and configure u-boot
-----------------------------------

The default SD card images include the u-boot firmware required to boot from
the card. Insert a flashed SD card into the DreamPlug and connect with screen:

    $ screen /dev/ttyUSB0 115200

Power up the DreamPlug and quickly press enter in the screen session to
interrupt boot. Then enter the following commands into the running u-boot
session (change the last argument of the 'sf write' line, in hex, if the .kwb
file size changes from exactly 196076 bytes):

    usb start
    fatload usb 1 0x6400000 uboot.2012.04.01-2_armel.kwb
    sf probe 0
    sf erase 0x0 0x80000
    sf write 0x6400000 0x0 0x2fdec
    setenv baudrate 115200
    setenv bootcmd '${x_bootcmd_usb}; ${x_bootcmd_kernel}; ${x_bootcmd_initrd}; setenv bootargs ${x_bootargs} ${x_bootargs_root} ${x_bootargs_console}; bootm 0x6400000 0x6900000;'
    setenv x_bootargs_console 'ttyS0,115200'
    setenv x_bootargs_root 'root=/dev/sdb2 rootdelay=10'
    setenv x_bootcmd_initrd 'fatload usb 1:1 0x6900000 uInitrd'
    setenv x_bootcmd_kernel 'fatload usb 1:1 0x6400000 uImage'
    setenv x_bootcmd_usb 'usb start'
    saveenv
    reset