Cool, I just noticed that on Windows 7 Media Center with a Hauppauge Nova 500 T Tuner card the red button works; so at last I can get Digital Teletext and interactive channels on the BBC without having to know their actual channel numbers (and as I remember they were actually ignored by previous versions of Media Center without a registry hack anyway).
This makes using MCE just like a standard Digital TV – should help general acceptance. This has certainly improved since the older versions.