Do you have a modchip in your Wii?
The update stops trucha signed content from working. This includes the Homebrew installer disk. It does not stop the Zelda: Twilight Princess hack however, so it is still easy to install Homebrew Channel IF you have Zelda for Wii (original or backup with a modchip).
Homebrew channel still works, there isn't much harm in upgrading unless you have modified disks (where you have modified the contents of a game eg).
For more info, and to download all the files needed, go to
Main Page - WiiBrew