Ok, so it's more of a hack than full compatability (they made it work by transcoding some of their videos to Sorenson as the Wii's version of Opera doesn't support the current Flash codecs, and the web UI isn't quite sorted yet), but it's a neat way to watch iPlayer stuff on the TV. And it means I won't need to fight Intel's graphics chips, which apparently only believe in the 'standard' 4:3 resolutions.
The next step that they're hinting at is an actual iPlayer channel on the Wii, which hopefully will be able to use something much better than Sorenson for the video.