In the Netherlands, there is a yearly list of the most rich people called "The Quote 500". Of those 500 richest dutch, I think about 15 are HFT owners and employees.

See: http://www.amsterdamtrader.com/2012/10/duyfken-sails-into-qu...

Depends. It is mostly a zero sum game, so all told $0. Of course, some people make lots and some people make -lots.

While intraday trading as a whole is zero-sum, the HFTs are taking profits from other traders, not from each other. HFTs as a group are profitable.

A good amount of HFTs fail. I've heard numbers ranging from 70%-90% of new HFTs fail within their first 2 years. Very similar to startups when you think about it.

Also, HFTs are most definitely taking profits from each other. In fact, in a lot of cases the faster, more successful HFTs kill off the new ones to the market. Not to mention there are a good number of predatory HFTs who exist solely to game other HFTs

It's hard to know how profitable HFTs are on the whole as for the most part they are very private. That said some very big names on HFT have recently laid folks off.

As someone who hires and interviews in this space, HFT firms seem largely the same as old trading firms were. Boom bust cycles that comer and go as profitable trades shelf life expire.