It’s astounding how quickly folks have begun hacking into the Wii remote, and after figuring out it’s a Bluetooth device, creating drivers and beginning to dream up apps for it on other systems. For a a lot of the latest, check out Liquidice’s Wii Hacks Page, Wii Linux, and WiiModWii. Some of these sites are being hammered with traffic (esp. Wii Linux), so try back if you can’t get through.
You can also search on “wiimote” on YouTube and find a lot of hack demos, like the above, which shows a guy playing Half-Life 2 on a Windows PC using a Wii controller.