Turns out retro photo filters and mobile photo sharing are big business. Just how big? Get this: Facebook has agreed to acquire 17-month-old Instagram for $1 billion in cash and stock. Instagram amassed 27 million users through iOS alone, but Facebook was likely motivated by the photo sharing app’s recent Android launch, which signed up 1 million new members in the first 24 hours alone. Just last week it was reported that Instagram had raised $50 million based on a $500 million valuation. Those investors scored a 2X return in less than a week.