BeerBorg

if you have a 2l yeast starter that has been spinning for 36 hrs (example).. is it safe to assume that the yeast are relatively evenly distributed in the sample and that pouring off half into a fermenter will net you about half the available yeast cells? (if not allowed to settle out first?)

Don't know the exact science or math behind it, but that's how I do it. I figure it's close enough.

Same here. I separate my very large starters into jars for use later and after days in the fridge settling, the yeast at the bottom are pretty uniform.

About right as long as it is a slurry all in suspension, if it settles out, then it gets a little more triccky to separate evenly.

That's how I do it. If possible I do it at high krausen, but as long as the bar is spinning and the yeast have not flocc'd out, your good.