Here are some registration stats by month:

We've generally had between 450-600 new registrations per month for years. Overall activity seems fairly constant so I suspect any departing member traffic is replaced by new member traffic. We're not expanding or shrinking which I would think is typical of popular niche websites. The same goes for subscriptions, with departing subscribers being replenished by newer members that subscribe. Subscriptions are down slightly 10-15% from a couple years ago but I would suspect this is a symptom of the current global economy. What really keeps us going are those who opt to subscribe for more than the required amount.