Call me cynical about the first option, but I find it highly unlikely that everybody figured out how to use the Facebook Platform; despite its low entry barrier many people are over-thinking it or simply trying to develop a Facebook application before they figure out how to build a web application in general.
The second option is far more likely, Facebook applications have reached such a level of ubiquity that "everybody and their mother" wants to write a Facebook application these days. Right now at a small consulting firm in Omaha, Nebraska some middle manager is asking his lead developer if the firm can reinvigorate their collaborative synergies and utilize the social graph to further meet their clients needs.
Facebook is the new Windows, and the Facebook Platform is the new Visual Basic and I feel as if there is a burden on "us" (the existing "top developers" on the platform) to start to cultivate a community that will encourage stylish, functional and ultimately useful applications on the Facebook platform, to ensure that there will never be a "Facebook 98" or a "Facebook ME".
Here's a couple of the best tips I can offer, and maybe Zach (developer of Free Gifts) can help expand.
- Learn by example: Currently Slide has many of the largest applications on the platform, and we've worked extremely hard tuning and tweaking our apps and understanding our userbase. When thinking about developing your application, it certainly won't hurt to check out some of the existing apps that have succeeded on the platform. Stand on the shoulders of others who have spent far more time researching and testing what works and what doesn't work on the platform than you'll be able to spend.
- Check out some demos: There are a few demo applications that you can dig through to better understand the basics of what makes a Facebook application.
- Just code already: By far the most common mistake I've seen thus far is over-thinking things, the majority of your questions will be answered by simply trying stuff out on the platform. This isn't high school calculus, you are allowed to guess-and-check. I am willing to help developers who obviously need it, but if you can't be buggered to try something out, I can't be buggered to point you in the right direction on where you went wrong.
With the first year anniversary of the original F8 event right around the corner in May, I feel we as a community of developers have made tremendous progress in establishing ourselves, but now I feel it's time for some introspection and self-improvement as a community.