I have a Wiikey and updated a minute ago. It doesn't change anything groundbreaking. As far as I know, the only bad thing about the update is that your Wii won't read the WiiKey Setup Disc anymore.
edit: oh yeah and I heared that US Wiiowners hat to accept a disclaimer that said that Nintendo is going to be allowed to brick your modded Wii. Doesn't mean they will, though