There are numerous reports on the
Wii forums of the screen blanking whilst playing virtual console games, but I haven't heard of any crashes during Wii games.
A reset seems to sort things out in most cases, and you can always check for firmware updates if your Wii is online.
Had mine since launch w/o probs, except for one VC game going to blank screen once.
Loving it, great fun.
Check out the
Mortal Kombat demo video on YouTube - really interested in playing that now!