Sharp eyed Google Analytics users (like our friend Stephen Trump, thanks for the heads up Steve!) will have noticed that there's been a big change right up front in your reports.
Google has, without little or no fanfare, changed the way they describe Visits and Unique Visitors.
Visits has become "Sessions".
Unique Visitors has become "Users".
Nothing else seems to have changed, so no need to panic if you simply use Analytics to report on website usage.
Combining Mobile App & Website Usage Data
If you're monitoring a mobile app in addition (or separately from) your website, this change is designed to somehow combine those two sets of data... I have no idea how that's going to work, but I'll be going along to SW Mobile on 20th May to pick the brains of Scott, Karl and the other clever bods there. If you have concerns about this change and how it affects your reporting for apps, maybe you should come along too.
Barry Schwartz' post on SEO Round Table (hat tip for the image)
Google Analytics' announcement on Google+ (probably why no one noticed it, right?)
Thom Craver's post on Search Engine Watch (further reading for analytics experts)