Following a tip from Steven S., I've hidden posts from friends' Facebook applications that don't interest me, resulting in a much cleaner home page. In only a month, I found that I have hidden more than a hundred (!) applications, which led me to wonder if Facebook shouldn't provide a reverse option, to only show certain applications instead.
To hide applications, I can imagine that there is a database query which has a
NOT IN () clause that rapidly gets longer. In contrast, to only show selected applications would require a much shorter
IN () clause that grows more slowly. From an engineering point of view, the latter solution would provide a more responsive system.
On the other hand, from a business point of view, encouraging subscribers to use applications would increase Facebook's stickiness and the number of ad presentations. If subscribers aren't notified about new applications (through their friends' application posts), they are unlikely to know about these applications.