4.2 System Update does not just destroy homebrew - destroys consoles
While Nintendo's message along with the Wii 4.2 System Menu Update suggested that the only thing which would be harmed in the update would be homebrew, recent reports suggest otherwise, stating that their Wii's have been bricked due to a glitch in the update.
The problem lies within the actual process of updating. boot2, used to boot the Wii properly, has been upgraded in the new update to change title IDs of channels to rid homebrew. However, this upgrade leaves means that boot2 has a much higher chance of causing write errors.
What this means is that when one goes to update their Wii, the process freezes and will not to continue the update. The system menu is unaccessible at this point. Pulling the Wii's plug out the wall will not help, either, as due to half-done upgrades boot2 will not be able boot up the Wii.
So while the original message was for Homebrew users, everyone may want to consider this now: Do you really want to risk the update to 4.2?
Update (1/10/09)
Nintendo of America have responded to the claims of Wiis being bricked, stating that if you have an unmodified Wii and your console has been bricked due to the 4.2 update, that they will try to help you if you ring customer service. If they find that your Wii is unmodified and has been bricked as a result of the update, they will provide a repair at no charge.
We'll all have to hope Nintendo of Australia follow suit and allow Australian consumers the same free repair American consumers can get if their Wii has been damaged as a result of this update.
Source: http://www.nintendoeverything.com/?p=24903