I don't feel quite as awesome as I did last summer when I tell people that I "develop facebook applications." Despite personally being really happy with my applications, I get the feeling that users now perceive facebook apps as spammy, poorly designed, and pointless. Sure, there are some applications that are knowingly like this (and they are probably making some quick cash), but to many new developers they just don't know any better.
The points in Tyler's post, as well as the ones below, will help new developers start on the right track and then we can all feel awesome again to be a facebook application developer. I am staying away from saying "don't spam" because that is a topic in need of it's own post.
Just because you haven't seen it doesn't mean it isn't there. Do a little research on existing applications with the same idea before you start development. This will help you decide whether you should pick up their best features and improve on them, or just scrap your idea altogether. There is definitely room for similar applications, but don't build a product if you can't make it better.
She may be hot, but she has no brain. Looks are great, but make sure you have a well built application to support your idea. Users love to uninstall when they see error messages.
Keep improving and adding features to your applications based on user requests, they really know best. I may be crazy, but I like to read and respond to nearly every (positive) comment and suggestion on Free Gifts boards.
Tyler pointed out that the one year mark is approaching, and the amount of progress the developer community has made is really amazing. Over the next few months there are a few things I really hope to see: inter-application collaboration, more functional user interfaces, and a decline of "one timer" apps (quizzes, etc).