I posted a comment on Facereviews.com and wanted to share it here as well.  I believe that the Future of Facebook Applications involve:

1. Better UI and usability.
From a visual/design standpoint, the Facebook Platform imposes a unique constraint – the frame around it.  It’s not exactly a blank slate.  The design of applications need to be more strategic to make it look coherent, consistent, and FB’ish. 

While developers focus on getting their applications out fast, usability and UI took a backseat.  There has yet to be a standard for design, but there will be soon.  As the good apps get better, FB Platform “Darwinism” will undoubtedly put the focus back on UI and usability.

2. Families.
Hands down the hottest company of 2007, Facebook is the chosen one – the one to rival Google.  But in order for that to happen, families need to be on Facebook.  Right now there is a lot of focus on friends and associates, but almost nothing for families. 

If they can get my mom and dad, and (gasp) my grandpa on Facebook, I will be amazed.  It’s a safe bet to say that Zuckerberg and Co. are aware of this and have many things under tight wraps.  The fast growing community of developers are also probably addressing this opportunity. 

3. Mobile advertising
One of the things that I feel FB does very well is using SMS to add/confirm friends and receive updates.  It works very fast and is dead simple.For all those who continue to speculate how they will monetize their platform?  Here’s the answer: mobile ads.  =)  

Nobody, not even Google, has really established any sort of leverage for the lucrative mobile ads industry.  Facebook, however, continues to create more leverage every day with new applications.  By using the built in FB SMS infrastructure, developers are able to create applications that send sms messages to users.  Furthermore, more and more people will have unlimited sms and data. 

So picture this:   SMS + FB Applications = A lot of SMS.  A lot of SMS = A lot of space for mobile text ads.  And if Google was any indication, text ads = $$$.     

Those are my 3 cents. =)