The latest firmware released for the Wii is reportedly bricking Wii consoles.
The 4.2 update released earlier this week, which killed off homebrew and other modifications is said to be causing problems for Wiis, not only with homebrew, but non modded Wiis.
So if you have 4.2 already, you’re safe, but if you’re on an older version of the firmware I wouldn't update anytime soon.