Here's what works for me:
guruplug:~# cat /proc/mtd
dev: size erasesize name
mtd0: 00100000 00020000 "u-boot"
mtd1: 00400000 00020000 "uImage"
mtd2: 1fb00000 00020000 "root"
guruplug:~# cat /etc/fw_env.config
# Configuration file for fw_(printenv/saveenv) utility.
# Up to two entries are valid, in this case the redundand
# environment sector is assumed present.
# MTD device name Device offset Env. size Flash sector size
/dev/mtd0 0x40000 0x20000 0x20000
guruplug:~# fw_printenv
bootcmd=setenv ethact egiga0; ${x_bootcmd_ethernet}; setenv ethact egiga1; ${x_bootcmd_ethernet}; ${x_bootcmd_usb}; ${x_bootcmd_kernel}; setenv bootargs ${x_bootargs} ${x_bootargs_root}; bootm 0x6400000;
bootdelay=3
baudrate=115200
x_bootcmd_usb=usb start
x_bootcmd_kernel=nand read.e 0x6400000 0x100000 0x400000
x_bootargs=console=ttyS0,115200
ethact=egiga0
ethaddr=00:50:43:01:5F:E8
eth1addr=00:50:43:01:5F:E9
x_bootarg_root=ubi.mtd=2 root=/dev/sdc1 rootdelay=10
stdin=serial
stdout=serial
stderr=serial
x_bootcmd_ethernet=ping 192.168.0.1
x_bootargs_root=ubi.mtd=2 root=0821 rootdelay=10
guruplug:~#
HTH, Jim