1/ At present we are including following yui2 libs on each page: dom, connection, container
3/ ajaxcourse, blocs, etc is using DOM, D&D...
4/ just search for "YAHOO."
There are only a few exceptions that use things not available in YUI3 yet (UI widgets), I think all DOM, D&D, ajax calls, JSON, etc. could be converted to YUI3 relatively easily before the 2.0beta. But not really sure, because I did not try the migration yet. Could you please try to choose just one selfcontained area and test the conversion YUI2->YUI3 there and estimate time/effort needed? thanks a lot.