To revert to the standard Linksys firmware, just follow the instructions in RecoverFromABadFlash and flash the Linksys firmware image (NSLU2_V23R63.bin) instead of the Unslung firmware image. If you do not have the firmware file, download the the original Linksys 2.3R63 zip file(approve sites) from Linksys web site (http://homesupport.cisco.com/en-us/wireless/lbc/NSLU2(approve sites) until the link is approved) and extract NSLU2_V23R63.bin.
Note that the process when going back from Unslung to Linksys is a bit more involved than the first upgrade, but is still easily achievable with no hardware skills required.
If you find that after you flash the original Linksys firmware on to the NSLU2 some or all of the web management pages do not work. Then you will have to go through the ResetSysConf procedure.
Please see the Warranty Statement for details if you plan on either reverting your device for a return (as either defective or doesn't do what you want).
There are currently two reported versions of beta firmware: a version R72 found here (link non-functional, 2009-02-05), and a version R73 available only from Linksys technical support.
Linksys Firmware versions collected over the years
These are originally Linksys released firmware versions, which I have archived and collected over the years. Folks wishing to roll-back or update to a newer Linksys released version my grab one of these files from my server.
(since the admins made it impossible to upload zip files or reference them externally, you will have to visit this external site http://www.ixquisite.com/nslu2(approve sites) to see and download the desired Linksys firmware version.)