Do not under *any* circumstances use the Linksys "EraseAll" utility to reflash your NSLU2.
In the worst case scenario, it may erase the bootloader and cause an unbootable slug. The only method of repair for the mentioned case would be JTAG, which requires extra hardware and knowledge that most users do not have.
Hence, it is *not* worth the risk using this software until Linksys address this issue, so you should use the Sercomm utility.
EraseAll is a utility provided by Linksys support for Windows, that provides the ability to 'manually upgrade' a NSLU2 to newer firmware. It actually erases and tries to rewrite all the contents from the NSLU2 flash, including RedBoot, the bootloader. If there is a problem during the rewrite of the bootloader, the NSLU2 will no longer be able to boot by itself and you will need JTAG access to the board in order to flash a new loader. Since you can safely upload firmware to the NSLU2 using either Upslug2 or the Sercomm Utility, there is no reason at all to use the dangerous EraseAll utility.