Hello,
I found a marvelous site which explains how to update automatically a SheevaPlug Globalscales to UBIFS.
http://plug.maisondouf.fr/doku.php?id=sheevaplug:distrib:ubuntuIt's in french. But the uboot command are universal

you have to update Uboot, save content of directory included in file sheevaplug-installer-v1.0.tar.gz in USB key, set some Uboot command, plug USB key, and reset PlugComputer.
There are just some little error on Uboot command. You have to change double quotation marks to no quotation marks for tow lines.
setenv recover1 'setenv mainlineLinux yes; setenv arcNumber 2097; setenv bootcmd "run recover2"; saveenv; reset'
setenv recover2 'run recover3; setenv bootcmd "run nand_boot"; saveenv; run recover5'
become
setenv recover1 'setenv mainlineLinux yes; setenv arcNumber 2097; setenv bootcmd run recover2; saveenv; reset'
setenv recover2 'run recover3; setenv bootcmd run nand_boot; saveenv; run recover5'
PS: in the file sheevaplug-installer-v1.0.tar.gz, you can change the rootfs.tar.gz and uImage files by the last available for SheevaPlug, and you'll have a new SheevaPlug in UBIFS with the lastest kernel

I've test it with the last 2.6.35.7
Regards