Today, news from the Warp Pipe project surfaced that their latest build was able to run Mario Kart: Double Dash!! at full speed over the Internet without a router. They hope to have a Beta version available soon (before the end of the year) with a full-featured client released early next year. You can download via BitTorrent a video of their program in action from their site. Check it out.
Nice work guys, but release that Beta already!! I can't wait to play some Kart races against real humans without having to use split screen (since I only have one Gamecube).