Is there any documentation that explains the best way to do writeback in a
cube? Specifically if you want to writeback a number of records at a time.
UPDATE CUBE works very slowly for one record, so I can't imagine it working
to well on multiple records at a time.

In addition what are the possibilities of changing dimension members in the
writeback but getting it to aggregate the correct value in the writeback? ie
for [Dim1].Leaf1 we have a value of 10 which is also the value of
[Dim1].Leaf1.Parent
we want this parent value to now be 20 by assigning a writeback value of 10
to [Dim1].Leaf3 rather than to Leaf1 so that the aggregate is still 20 but we
have some sort of audit trail in the writeback.

Thanks