Short story: when the GameCube mic is connected to the Wii and you try to run unsupported games, they will hang at startup.
Long story: when some years ago I went in Japan for the first time, I bought a Wii and a lot of GameCube games, as they were sold for just 100 yen cadauno (around 80 cents at the time)
I also bought ä¼èª¬ã®ã‚¯ã‚¤ã‚ºçŽ‹æ±ºå®šæˆ¦ (Densetsu no Quiz Ouketteisen - The legend of the quiz tournament of champions), a quiz with voice recognition where you have to say the right answer, in Japanese and without a list of "possible" answers.
Ok, I never played it, but the box is nice to keep on my shelf... and then there was the very useful mic included in the box 
The games that use the mic are:
- Mario Party 6
- Mario Party 7
- Odama (a "ninja" themed pinball created by the designer who created the only Dreamcast game that uses the mic)
- Karaoke Revolution
In the beginning, I only owned GameCube games: Wii games were "too new" and were starting from 2000 yen - $15, so I preferred to save money and buy 20 games for the same price - I didn't even have Wii Sports, as in Japan it's not bundled with the console.
When I came back to my country, to play PAL games I installed the WiiKey.
The problem is that the Japanese Wii works ONLY in Japanese.
Yes, if you take a copy of the Italian Wii Sports DVD and you run it on a Japanese Wii (using a modchip, because there is regional lock), everything will still be in Japanese!!! (unless a game does not contains the files required for Japanese language)
So, when on Waninkoko blog I read about his new Region Changer, I immediately using for changing the region to PAL.
What a dumb decision! It was an untested beta (Marcan defined it as semibrick) and I got an half-working Wii tthat would hang when the keyboard would open because the Italian dictionary wasn't installed, and had double channels for weather, news, and so on...
A mess!
In the end, using AnyRegion Changer I fixed the problem, but I never managed to run any of my GameCube games anymore.
I tried everything, loaders, dozens of different MIOS, but ALL my GameCube games were hanging at boot: strange....
I tried using a GameCube SD adapter to load them using the old SD Loader: nothing
I tried the new DIOS MIOS, for loading games from USB: nothing, no game started
Yesterday I told myself: "enough, there is no way to make them work", and, while I was disconnecting controllers and memory cards, including the mic (that's actually using the memory card interface). Just when I unplugged it, BOOM, the game started!
I tried my games: all were working now!!!
Moral: when the GameCube mic is conntect to the Wii (at least to mine) and you try to run a game that doesn't use it, it will hang at the booting logo.
Yay, now I can play Donkey Konga
!