Instagram has more then 7m users & just 5 employees

"After 10 months in the App Store, Instagram has grown to a community of over 7 million people. In that time, we’ve grown from 2 people to a team of 4, and today we’re excited to welcome the fifth member of the Instagram team, Jessica Zollman (@jayzombie). Jessica joins as our Community Evangelist, where she’ll help nurture all aspects of the Instagram community. That includes everything from community outreach to holding events, to writing on our blog, to helping people with their technical support issues, to helping write copy for future launches."

Source:  Instagram blog, 10th August 2011