For Metafilter, at least – I think the joining fee is mostly to encourage higher quality participation.
Matt Haughey – the creator of Metafilter
The $5 one-time fee to participate (beyond reading for free) isn’t really part of any business model. It doesn’t bring in enough revenue to even cover hosting costs, but it lessens the load on myself and the other moderators, it
virtually rids the site of drive-by fly-by-night spammers, and it helps make sure people really, really want to be
there.
Metafilter and Pinboard have approaches which may work — small, upfront cost for joining, something to offset hosting fees. Pinboard
For Metafilter, at least – I think the joining fee is mostly to encourage higher quality participation.
Matt Haughey – the creator of Metafilter
via http://blog.metaprinter.com/2008/12/metafilter-founder-matt-haughey-qa-including-a-few-newspaper-answers/
If someone’s entire invite tree is at risk, that’s presumably not an issue here