Other developers feel it's too early to gauge whether there is serious money to be made from Facebook applications. "I'm trying to remain cautiously optimistic," says Blake Commagere, who has helped to create several Facebook applications. "I'm not as bold as some of the people that will claim 'Application XYZ is worth US$10 million.' I won't dispute that there is value in a lot of these apps. But US$10 million is a lot of money."
Price says he doubts that his My Room application would have become popular had he and its co-creator devised it from the beginning to make money. "We do not believe that if it was ad-based and focused on generating revenue we would have achieved the growth we have. We have considered ways to generate revenue, but currently we are consumed with the effort to make our users happy," he says.
His advice to others interested in making a Facebook application? Build something for the love of it. "In the end, receiving e-mails from users who share your same love for what you built is very satisfying," he says.
Third-party developers offer the following tips on how to make a popular application for Facebook:
1. Target the friends list
One of the biggest draws of developing an application for Facebook is the unprecedented access to the social networking site's massive user base -- its so-called "social graph." Developers can reach a broad audience with very little effort.
"Typically, software developers struggle to get anyone to use their products, regardless of how useful," says Haroon Mokhtarzada, CEO of Freewebs, which created the medieval fantasy game Warbook for Facebook.
So the developers of the most successful applications say to exploit the social "interconnectedness" of the Facebook user base. It can be used to target the demographic you want to "sell" your application to.
"Facebook doesn't give you all the different social graphs of data that it has," Commagere explains. "The friends list is the most readily accessible one, but many others can be calculated. I could construct a query against Facebook servers that determines 'friends that love movies.' I can do things with the results of that query, like encourage [the user] to interact with these friends through an app that features movie-related stuff, like 'Send a movie quiz to these three friends because they love movies like you!' What you can typically query is always a subset of the friends list."
2. Make it sticky
Create an application that encourages people to interact with it frequently -- something that is useful, fun or addictive by design. Applications that are "set and forget" (such as one in which the user simply puts together a list of favorite friends, movies, music or other items) can quickly fall into disuse.
"Growing daily active users is far more important than total users," Mokhtarzada explains. "Utilize Facebook's social graph to make the application interesting to people."
3. Make it social
Price, who works as an interior designer, says he loves how Facebook brings people together. So he and a friend who is also an interior designer created the My Room application to exploit the social aspect of Facebook. "As interior designers and developers, we wanted to create an application that would bring together those who share a love for design," he says.
Likewise, Flixster created Movies to bring together people who love movies. "Flixster is all about a person's personal relationship with movies, sharing, rating, reviewing and discovering movies through friends and friend recommendations. Facebook is the perfect environment for our application, where so many people are already connected with their friends. We have seen our application taking off and working so well in that environment," says Flixster's Polsky.