Twelve months notice
cdixon.org
cdixon.org
It took about ten months from start to finish, but they appreciated the openness, honesty, and (most importantly) hard work that I put into the company prior to emigrating.
Were we a startup? Um. No, more a small player. But I would have done this whether it was a small company or a large company because I respected the people I worked with. If I didn't respect them, then they'd exactly get the two weeks (and that happened more than once, too).
In his defense, he was fresh out of college and thought it wasn't that big of a deal. So I sat down with him and explained that it WAS a big deal for a company our size, and he was super apologetic.
In summary: Don't screw people over unless you work in an anonymous, transactional industry, which startups aren't.
When I took a position with a small company way back when, I told them up front that I had a summer job working for my dad for 3 weeks each year. They were very accommodating.
This does not address the lack of time off for a vacation, but that is another post...
I've found through both first- and (close) second-hand experience that this generalization doesn't hold.
The OP's poing about assessing openness and honesty of the management is well taken.
The advice I generally give is also Golden Rule based, which is to give the amount of notice one reasonably believes would be given in a layoff. This is, of course, easiest with a company that has already gone through such a thing, having already set an expectation.
I've found the freedom to be unabashedly open about my search for fulfillment in my work to be an incredible source of inner peace and job satisfaction. It's humanizing.