Here's a list of steps to get you started with the Guru Plug. It's basically a summary of information scattered across various websites. I'm mainly using this as a reference for myself but I'm posting it here in case you might find it useful, too. This page may be updated without warning.
Since the OS that comes installed with the device is outdated, you should update. Get the latest U-Boot (uboot.guruplug.bin), Kernel (uImage-guruplug) and RootFS (rootfs.ubi.img) images from the official download site and copy them to a FAT formatted USB stick.
Connect the JTAG adapter to the Guru Plug and your computer. Use screen or any other terminal emulator to access the plug:
screen /dev/ttyUSB0 115200
usb start fatload usb 0:1 0x0800000 uboot.guruplug.bin #type 1:1 if you're using the lower USB port nand erase 0x0 0xa0000 nand write 0x0800000 0x0 0xa0000 reset
usb start fatloat usb 0:1 0x6400000 uImage-guruplug nand erase 0x100000 0x400000 nand write.e 0x6400000 0x100000 0x400000
fatload usb 0:1 0x6400000 rootfs.ubi.img nand erase 0x500000 0x1fb00000 nand write.e 0x6400000 0x500000 0x(SIZE_IN_HEX) reset
The plug should reboot into the new operating system. Login as root via WiFi or JTAG (user: root, pass: nosoup4u), then perform the following maintenance tasks.
rm /etc/ssh/ssh_host_* dpkg-reconfigure openssh-server
/usr/bin/uaputl sys_cfg_ssid $SSID
Right below that, insert the following lines to set up WPA2 encryption:
/usr/bin/uaputl sys_cfg_protocol 32 /usr/bin/uaputl sys_cfg_wpa_passphrase "yourpassword" /usr/bin/uaputl sys_cfg_cipher 8 8
echo "newhostname" > /etc/hostname
aptitude install rdate rdate ptbtime2.ptb.de
aptitude update aptitude upgrade
Remember that you just changed the SSH host keys so you should get a warning when you try to log in using SSH. Remove the violating keys from your ~/.ssh/known_hosts file and you should be fine.
Unfortunately, there is a serious problem that causes the plug to crash and reboot once both LAN ports are in use and one of them is attached to a Gigabit device, even with the latest images. Thus using it as a combined WiFi/LAN router is currently impossible. Discussions in various forums suggest that this may be caused by the plug overheating which I can confirm. I cooled the plug using a large desktop fan, plugged in the Gigabit and it worked without problems.