If you've switched your iOS calendar use to the usually pretty excellent Cal by Any.do, you'll want to take note. Somehow the dates have gone wild, and apparently today is Sunday September 7 2013. Only, it isn't. As we all know.
Event dates created elsewhere, such as on Google Calendar, aren't altered to match the date Cal is showing. For example, if I pull up the details I've added to a calendar outside of Cal for my return journey today from Berlin, the event details still show correctly Sunday September 8. But that doesn't help the confusion of looking at the calendar and the dates being wrong from now until as far ahead as you want to think.
Hopefully it'll get fixed soon enough, and I'm not sure when exactly the dates started to go wrong. But for now, you might want to double check if you're relying on Cal to manage your calendar on your iPhone.
Update: Thanks to a couple of iMore commenters, it seems this issue isn't affecting everyone. It still remains on my own device as per the image at the top of this post, but if you're seeing it too be sure to shout out in the comments below.
Update 2: See comments below for a fix to what seems like a small bug. Thanks Snaab4!