...now busily buying every microSD card they can get their hands on and testing it in their phones, and when they have a list of which cards perform well enough to recommend they'll be distributing the information.
That is certainly a 180 from previous positions and we think Microsoft gets it here: the cat is out of the bag and users will try to swap their cards, regardless of the dire warnings on internet blogs. Going into more detail, Microsoft's senior product manager Greg Sullivan described the issue more succinctly:
Yes, it's about read write speeds [which is what the SD class number indicates]. The IO rate is part of it but actually what's equally important are the bit error rates. That will impact the speed of the checksum rewrite.
On the one hand we feel bad Microsoft has to go through with all of this, but on the other, this was a situation clearly not well managed from the start. The reason given for the mishandling is an old one: time. Microsoft simply did not have enough time or resources to test all the cards before launch. At least it appears they are owning up to the matter now and we can look forward to a "recommend list" in the future.