Retailers are fond of blaming sales slowness on "the weather." It might have been too warm when they were trying to sell coats, or too cold when they were trying to sell swim suits.
Sometimes the sluggishness is more protracted and worrisome, as some suspect might be behind Google's fourth-quarter revenue growth figures.
To be sure, growth has been decelerating for some time, as the law of large numbers kicks in: it just is mathematically harder to sustain high percentage growth off a large base, compared to a small base.
But some observers also detect a slowing of use by established social networkers as well as a slowing of new adherents. In part, that might be the law of large numbers starting to kick in as well. The other issue is how soon saturation is reached for the current generation of social networking sites.
Users with high interest joined early. Later users presumably have less intense interest. Something else might be happening as well. People discover over time which tools are really useful and which are less useful. As users experiment with the various sites, they probably are settling in to more established patterns of use. Instead of meandering among a number of sites, users will discover over time that one or two sites make the most sense, and will gradually cease using the others.
Saturation is an issue in every market.