Ok, I installed r48 today and before that I had r44 installed. I have to note a few things:
With r44 (Mario kart running):
Pressing On/off causes wii to shutdown
Pressing reset fades the screen to black and then either freezes the wii or displays a gamecube message that an error has occured and stuff...
With r48 (Mario kart running):
On/off and reset behaves like r44
Using L+Z+Digital-Down+A causes wii to reset
Using L+Z+Digital-Down+B causes mario kart to return to the "press any key to start" screen
I have a white wii with 4.2E and a d3-2 drive. My SD card is a 2GB Sandisk and never had any issues with that.
I have priiloader 0.7 installed with some hacks but I don't know if that is related. Lastly, I have to note that although most of the times my gamecube games start fine, from time to time running a game causes two vertical stripes to appear on the left side of the screen and the wii freezes.
I'd be glad to provide any details if anyone wants to look into it.