A third is a lot, yes, but not impossible, no.

I would say that people who sign up for Pinboard (+ pay ~$10) are much more likely to support a service that they like and rely on. Otherwise they would've chosen a free service like Diigo or Delicious to begin with.

English is not my first language, so I'm not sure. Does "makes $200K every year" mean net profit or just the income from which hosting still has to be subtracted from? If it's the latter, that means a lot more people are paying for archive.

The $200k is the income (revenue). Monthly expenses have been published in the past, most recently (AFAIK) for 2012: https://docs.google.com/spreadsheet/ccc?key=0Au7yiR802qQmdDJ...

He even has health insurance!

I remember Maciej saying he collocates his servers, which works out to be remarkably cheap in the long run. I'd assume the server costs are actually pretty small, relative to the income of the site.

Those costs are public. See https://docs.google.com/spreadsheet/ccc?key=0Au7yiR802qQmdDJ...

The link is for 2012, but they haven't changed much.