Depending on how old the article is, the flag can either drop it by hundreds of places, or at least 10 places for a couple of flags. I have done some testing (a while ago), and found that having 2 people flag one of my articles when it had 40/50 points dropped it by 10 places in the next 5 minutes. Unflagging it restored the original position.

Newer articles with fewer points get a much more dramatic effect, however, as far as I can tell.