Thanks for all the info. For whatever reason, even though I usually have no problem finding and sorting out information about complicated and controversial topics, I find this one (i.e. the general topic of Jewish religious and ethnic divisions) very difficult to systematize, and your comments have clarified a lot. Of course, even I was much more knowledgeable about the topic, I'd still consider it a valuable opportunity to hear the perspective of someone who has some insider knowledge but nevertheless strives for objectivity.