I am using NW6.0sp4 with AFP and CIFS clients.
I recently downloaded and tried NW6.5sp1 for evaluation, and found that AFP
is upgraded to 3.0 and stores Mac filenames in Unicode ( good, a huge file
over 4GB can be saved ! ).
But there is a compatibility problem between AFP and CIFS in diacritic mark

Mac OS X uses non-composed form of Unicode as its filenames, while CIFS
uses precomposed ones.
For example, if a Japanese character 0x30ac is used by a CIFS client as a
part of a new file name, it can also be accsessed by AFP clients as 0x30ac.
In case of AFP client, however, the same 0x30ac is separated into 0x30ab +
diacritic mark before sent to NW server. As a result, it cannot be seen
correctly by CIFS clients. ( The charactes looks exactly the same from
users on both sides .)

Mac OS X sever takes care of this problem ( probably, by separating
precomposed Unicode on server side, etc. ) and I beleieve the same kind of
consideration is necessary.