I'm not convinced it was an over the air "update". Maybe just a command to activate the button or service. We did have an update recently, maybe that's where it came from. And maybe they just scheduled the feature to appear yesterday.
Or maybe the feature was always there, and when .mac and your iphone sync'd yesterday, .mac showed the "_galleries" directory (which I don't recall seeing before, and is probably new) and the iPhone unhid the button.
Don't go rushing to put on your tin foil hat just yet.