If you've seen some position/ranking shifts on Google the past few weeks (and drops or increases in traffic as a result), you're not alone.
Early indications are that the recent fluctuations in the search results are simply Google making core algorithm updates (it makes 500-600 updates each year by the way). The sometimes volatile nature of the changes, however, has driven many SEOs to speculate (often wildly) whether the recent changes weren't actually Penguin-related.
Google's Gary Illyes, however, did confirm this week that it was a core algorithm update and not Penguin. Many SEOs remain concerned that a Penguin update (the focus of which is links/citations) is ultimately coming though and expect it sooner rather than later. With the holiday shopping season behind us, it's a good time for Google to make that change, and SEOs know it.
As always, if you're pursuing quality relationships with other websites that result in a link, and developing content that is useful to and compelling for your audience, the only way to move on the SERPs is up so... don't panic.