[CORRECTION] 7742 went dark out of the 8299 that committed. Interesting to note: 204 of the top 250 subreddits are dark (src: save3rdpartyapps.com). ( reddark.untone.uk )
As of 12:56pm GMT (7:56am central time), 7742/8299 subreddits are no longer public
The information I initially posted is misleading. Thus, I have edited the title and this content area to report accurate numbers.
As @roofuskit mentioned, the 8299 number is the amount of subreddits that committed to going dark, not the total number of subreddits, which is over 3,000,000.
And as @8thiest was keen to observe, 204 of the top 250 are dark, as you can see from this site: https://save3rdpartyapps.com/