Reddit is kind of a notable standout. Maybe that and Twitter's features are what guarantees a sustained viewership. I don't know, this is all kind of new.
At least for photo and video sharing sites, it seems like these tend to be trendy and have a population boom and bust cycle. But then again I don't want to speak authoritatively. But looking at FB it reported it's first decline in daily visits this year and the decline among teens and younger generations is even more pronounced. Certainly looks like a population peak.
