After hours of confusion and reading tons of posts I finally figured out that replacing PHP 4 style object creation, where new is assigned by reference:
$node_obj =& new someClass($somearg, $moreargs);
which in PHP 5.3.0 generates an E_STRICT message telling you that "Assigning the return value of new by reference is deprecated"
with the following, where & has been removed:
$node_obj = new someClass($somearg, $moreargs);
in some cases (at least in recursive loops while creating a tree of nodes containing child nodes) requires
before the actual object assignment line to avoid all child nodes becoming identical.
Hope that delicate piece of information will save someone else a few hours.