another reference, i organised a conference of their franchise a couple of years ago: http://www.isea-web.org/
they are an independent unaffiliated organisation, with elected board members, but, their secretariat is supported by a university in the UK, who basically have allotted x hours/week for one faculty to be the secretary. the paid secretary is not a voting member in any decisions, but their presence ensures continuity and institutional memory. the secretary is not elected, and i suppose the board could change the secretary and the institutional affiliation through voting, if they wanted.
edit, the financial model: the local organisers pay a ‘license fee’ to the society to host the conference, and take care of the budget themselves. the logic here is that the brand of the society makes it easier to get sponsors etc (which really wasn’t the case!). in return, local organisers have a freedom to decide on the content (program committee and keynote speakers), and the society oversees and has the right to approve/suggest changes to the local organisers’ plans before they are allowed to go ahead.
