Where are you getting the idea that apps are counted as users from?

The story pretty clearly says "500 million people".

    *  More than 500 million active users
    * 50% of our active users log on to Facebook in any given day
    * Average user has 130 friends
    * People spend over 700 billion minutes per month on Facebook

# More than one million developers and entrepreneurs from more than 180 countries # Every month, more than 70% of Facebook users engage with Platform applications # More than 550,000 active applications currently on Facebook Platform # More than one million websites have integrated with Facebook Platform # More than 150 million people engage with Facebook on external websites every month # Two-thirds of comScore’s U.S. Top 100 websites and half of comScore’s Global Top 100 websites have integrated with Facebook

http://www.facebook.com/press/info.php?statistics

They aren't going anywhere for awhile, this is exactly why I've spent so much time developing apps JUST for FB.

And are they successful? Do you make money from them (if that's your aim)?

So the average user spends 1,400 minutes on facebook each month - about 23 hours and 20 minutes, or about 45 minutes a day. This figure could be really skewed if it tracks log-in time, not actual eyeball time (although that seems unlikely to me, looking at the daily number), and a lot of usage is probably games, but it's still massive, and, to me, somewhat disturbing.

Still less time than TV (2.8 hours/day[1]), though.

[1] http://www.bls.gov/news.release/atus.nr0.htm