Of course the user base is shrinking.  After a certain age, we are all getting bit shorter due to osteoporosis or sarcopenia :)

However, for a serious answer, I just feel that less are socially active or have different social outlets, so lack of participation might be a caution but doesn't necessarily mean that users are dying out.  Anything we can do, as a collective all over the poserverse, to interact in a postive way with newcomers, will sow seeds for an active community.

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