Since photo-sharing iPhone app Instagram launched version 2.0 in the App Store last week, users have been signing up in record numbers. Now, the service is seeing a sign-up rate of over one user per second, or roughly 78 per minute. Co-founder and CEO Kevin Systrom says Instagram hit a new peak upload record on Monday with 26 photos uploaded every second.

Instagram is having an impressive run. In less than a year since launching, Instagram has amassed more than 10 million users, including celebrities like Snoop Dogg and Justin Bieber; comparatively, Facebook, Twitter, and Foursquare, all hot start-ups at one point, each took over two years to reach the same 10 million user mark. Even more remarkably, Instagram has achieved this user base while only being available on a single platform: iOS.

By the way, Instagram still only has six employees.

Instagram launched back in October 2010, but back then, the company was trying to pivot out of another venture, a Foursquare-style location service called Burbn. The reason for Instagram's success was part-good product, and part-good timing. The first Instagram app launched pretty soon after Apple released its iPhone 4, which was advertised as having a much better camera than its predecessor. With high demand for a good photo sharing service on Apple's new platform, Instagram stepped up to the plate.

The first iteration of Instagram allowed users to take pictures, add smart effects and filters, and upload the photos through Flickr, Tumblr, and Facebook. At this point, no one had achieved this level of interconnectivity with other platforms.

Many services like to keep content to themselves, but we like to push it out to other services, Systrom said. That was a real pain point for people, and that's one of the things that made us stand out from the beginning, I think.

The speed at which the app runs also gave Instagram a competitive advantage.

When you're with a friend at a café or whatever, you don't want to waste five minutes waiting for your phone to upload a high-resolution image, Systrom said.

By providing lower-resolution images than its competitors, Instagram made the photo upload process much faster, and the app also started uploading the photo to the service before the done button was clicked, making the app even speedier.

In Instagram Version 2.0, Instagram is focused on, yep, more speed. Instead of a separate menu of filters, filters can be applied even before the user takes the photo. Since filters take less time, the company felt comfortable to enough to accommodate higher-resolution photos.

Therefore, for anyone who wants to print out and hang out their Instagram photos, Instagram 2.0 features larger images for print and framing purposes, and the ability to rotate images, add or remove borders and tilt shift, or blurring a section of the photo.

In a space where a lot of people are trying to attack the same problem, we think our goal should be to really lock up the space, Systrom said.

Instagram's application has always been free, but the company is still trying to find ways to monetize the service. There's no word if Instagram will launch applications for Android or Blackberry, which would definitely benefit the company's overall revenue strategy. In the meantime, the company will just have to make do with its recent $7 million round of funding.