JMan on 01 May 2010
Depends on how 'clean" you want it. If you don't want access to the homebrew channel, just delete it. But Nintendo can detect that you hacked your Wii and that can void your warranty if you still have one. See this article about somebody who used a utility to completely clean their wii before sending it into Nintendo for repairs:
http://hackmii.com/2010/04/check-disk-for-pre-repair-process/
