In a statement this afternoon, Microsoft said it estimated the error had affected at least 8.5million machines or one per cent of Windows computers worldwide. I've never known anything like this, and I've been around for a long time.
Edit to add that some PCs are encrypted with Bitlocker - and not everyone has the recovery key.
What we also don't know is why a buggy driver file can cause repetitive BSODs - which led to another problem in that affected PCs have to be logged into safe mode to delete the file. I presume that choosing the "Safe mode with networking" is not an option as the buggy file would be loaded, a pity because this option would enable a small script file to be downloaded and run to navigate to the file and delete it.