I see from http://cryptofresh.com/witnesses that we currently have 27 active witnesses, with the rest on standby. How is this number determined, and what can move the threshold between active and standby?
It's weighted median or average number of votes on witnesses.
For example (maybe not as accurate),
* if only one stake holder is voting, if she votes for 27 witnesses, then there will be 27 witnesses.
* if only 2 people with same stake is voting, one votes for 27, another votes for 23, then the result will be 25.