Detecting the Opera web browser is easy as it's the only browser to implement the
window.operaobject. The Nintendo Wii console has an Opera web browser but until yesterday I had no idea how to recognise it as different to the PC version of Opera without looking at the user agent string, which can be easily spoofed.
It turns out, however, that Opera on the Wii has extra objects that allow access to details of the Wiimotes --
window.opera && opera.wiiremote.
Of course we can do much more than just detect that we are running on the Wii. As far as I can tell the only thing that can't be detected are the values from the accelerometers. There are a number of demo pages as well as a simple game called Wii Roll that you can try.
Of course you can't develop web pages on the Wii so testing web pages will mean trekking backwards and forwards between your PC and the Wii. Of course someone else has already thought of this and developed a
wiiremoteemulator script so that you can develop and test on your PC.