I'm seeing changes in one of my informational niches (which rarely sees changes when everyone else around here does). I've actually moved up on a few terms for which I've done some on-page optimization recently, but only in ways that also improved the content's usefulness to visitors.
But I'm suspecting my top competitor, who used to be #1 for nearly all queries in our niche, has just lost some ranking. Suddenly they're not #1 every time, but worse, in a case or two they're being outranked by irrelevant sites.
Additionally, on several queries where my competitor has a good useful page on [search term], they're not appearing at all unless you add their domain name to the query, and then you get a sort of navigational page in which the link to the [search term] page can be found, but not to the actual page itself. Very strange.