There is two minor software updates (at least in Europe) for Virtual Console games. I saw this when I went to the Shop Channel.
Mario Kart 64:
“The new version fixes minor error that occurred when the player selection screen was left running for too loong.”
“The new version addresses certain issues that players experienced with the original version of the game relesed in December 2006.”
So it looks like just small bug fixes, but it’s nice to know that Nintendo addresses this problems. I would be nice if Nintendo could fix it so you where able to save ghost data in Mario Kart 64.