Below is a graph that shows the total number of distinct entities filing a 10-K or 10-Q over time. It also shows the number of distinct entities expressing "substantial doubt" for the first time in one of those filings
Click on graph for larger image in new window.Note: Left scale doesn't start at zero, and the right scale is a 4 quarter average.
These are just initial expressions of "substantial doubt".
On a cumulative basis, a stunning number of filers are expressing concerns (more to come on this). For details, see SEC data guy's post.