In the E14 webinar Q&A at about 43:40, Eben appears to say that the Pi has a fixed 3.3V SD interface. If that is the case then it is a mistake ever to attempt the SDR/DDR modes. But the DS/HS modes should still work at 3.3V on all cards?
May well be true: the boot problem the puppy linux folk have ( http://www.raspberrypi.org/for.....emu#p62087
) and their boot screen (http://i.imgur.com/TX3i6.jpg
) indicate the Pi is indeed failing to switch to 1.8V
sdhci: Switching to 1.8V signalling voltage failed, retrying with S18R set to 0
It appears that then hangs. So in the short term if we hard code sdhci to not try any fancy modes could allow use of higher spec cards but in compatibility mode. And in the medium term maybe get 1.8V signalling (fixed?).