I love Instagram [3]. At first I was skeptical about yet another photo-sharing app, but as soon as I started using it I discovered an entire social network around photos. Now I check in daily for a few minutes, just to browse around through the photos of people I follow. It's just as fun as keeping up with Twitter, except there is less noise and more serendipity in my Instagram stream. I do not use many social media products beyond StockTwits and Twitter, so that says A LOT about how captivating Instagram is.

CEO Kevin Systrom and the Instagram team are exactly what you picture when thinking of scrappy startup entrepreneurs: four guys in a room. Literally, there are only four people at Instagram. And they're working in a corner of a shared tech office in San Francisco's South Park neighborhood. While the company has raised millions in capital and is watching its user base grow at the astronomical rate of over 1 million users per month, the team isn't getting ahead of itself; they haven't even gotten around to building a Droid app yet. So what's the game plan at Instagram? I stopped by to find out.

Last week on Co.Location: How Meetup Helps Online Communities In The Real World [4]

Howard Lindzon [5] is the co-founder and CEO of StockTwits [6]--a social network for traders and investors to share real-time ideas and information. StockTwits was recently named one of the 10 Most Innovative Web Companies in 2011 [7] by Fast Company and one of the 50 Best Websites [8] by Time magazine.

Read More: Most Creative People 2011: Kevin Systrom/ Instagram [9]