DISQUS

...yes... but... ;)
In return for poor documentation, Facebook will give you promotion on their "Recently Popular" list way before your app is ever really too popular...
In fact, once it is very popular, you're not likely to get a spot on the Recently Popular list - as far as we can tell
(check out the recent histogram on http://apprap.blogspot.com which maps the recently popular list to the most users list)

Superlatives had a 113% average daily growth rate from July 11 through July 17th (675% growth during that period)... which was the first period we could track, so it didn't pop up on our radar of consistent growth... so if apples-n-oranges had time to improve on that, they should get at least an early spike...
(btw - your blog rocks for FB fanatics)

Books iRead had a 14% growth rate during the period of July 6-11... They added 12,000 users on their (then) base of approx 86,000 users... so they're doing ok, but not in the top 101 in terms of growth rate or momentum...
More stats at http://apprap.blogspot.com (but we haven't yet categorized to compare all the 'books' apps, for example... )

fwiw... We're starting to track detailed stats on the facebook apps at http://apprap.blogspot.com ... might be a good companion to comscore's more general stats...