If we have two users A and B, both with OOo 3.0 opening a Microsoft .xls or .doc
or whatever file on a Windows or Samba share, they can both open it R/W and
neither will know the other has it open. Both can update/overwrite each others
files and get no warning this has happened.

Similarly, if user A has 00o 2.x, and user B has OOo 3.0, this behaviour is
shown opening native ODF files or .xls, etc. files. User B opens the file as
R/W, user A can also open the file R/W. Both can overwrite each others data and
never know it has happened.

If an Excel user has an .xls file open, the OOo 3.0 user can open the file R/W,
make changes, but is then unable to save the changes without doing a Save As
(shows general I/O error).

When testing, I tried multiple settings for file locking with the Samba share,
but was unable to come up with anything that would alleviate this behaviour.
Standard setup for us is oplocks = yes, level 2 oplocks = yes, veto oplocks on
.xls files (tried with this off and made no difference), strict locking=no
(tried with this option as yes and made no difference), csc policy = manual