When creating a file on CIFS-mounted file system (using Unix Extension), file do not inherit default POSIX ACL for "other".  However, directory created in the same fashion inherit it just fine.

Client (intrepid-desktop in the example below): 
 - Ubuntu 8.10 (currently alpha), kernel 2.6.27
 - Samba from the distribution: 3.2.3
 - cifs kernel module v. 1.54


Server (intrepid-server in the example below):
 - Ubuntu 8.10 (currently alpha), kernel 2.6.27
 - Samba 3.3.0pre2 compiled from source (default ./configure, no option)

On the server, smb.conf is completely blank (all default), except for the share definition:

[share]
    path = /srv/share
    read only = no
    inherit acls = yes


Example (this part on the server):

ubuntu@intrepid-server:~$ umask
0022
ubuntu@intrepid-server:~$ cd /srv/share
ubuntu@intrepid-server:/srv/share$ sudo mkdir test-acl
[sudo] password for ubuntu: 
ubuntu@intrepid-server:/srv/share$ sudo chown ubuntu:ubuntu test-acl
ubuntu@intrepid-server:/srv/share$ setfacl -m d:o:rwx test-acl
ubuntu@intrepid-server:/srv/share$ getfacl test-acl
# file: test-acl
# owner: ubuntu
# group: ubuntu
user::rwx
group::r-x
other::r-x
default:user::rwx
default:group::r-x
default:other::rwx

ubuntu@intrepid-server:/srv/share$ mkdir test-acl/dir-local
ubuntu@intrepid-server:/srv/share$ touch test-acl/file-local
ubuntu@intrepid-server:/srv/share$ getfacl -R test-acl
# file: test-acl
# owner: ubuntu
# group: ubuntu
user::rwx
group::r-x
other::r-x
default:user::rwx
default:group::r-x
default:other::rwx

# file: test-acl/test-local
# owner: ubuntu
# group: ubuntu
user::rwx
group::r-x
other::rwx
default:user::rwx
default:group::r-x
default:other::rwx

# file: test-acl/dir-local
# owner: ubuntu
# group: ubuntu
user::rwx
group::r-x
other::rwx
default:user::rwx
default:group::r-x
default:other::rwx

# file: test-acl/file-local
# owner: ubuntu
# group: ubuntu
user::rw-
group::r--
other::rw-


So far so good, the file test-acl/file-local inherited "other" permission from the default ACL as expected (not inheriting x is expected, as explained in acl(5)).

Now, on the client:

ubuntu@intrepid-desktop:~$ uname -r
2.6.27-2-generic
ubuntu@intrepid-desktop:~$ modinfo -F version cifs
1.54
ubuntu@intrepid-desktop:~$ umask
0022
ubuntu@intrepid-desktop:~$ grep intrepid-server /etc/fstab
//intrepid-server/share /home/ubuntu/intrepid-server    cifs    user,username=ubuntu,password=ubuntu,noperm     0       0
ubuntu@intrepid-desktop:~$ mount /home/ubuntu/intrepid-server
ubuntu@intrepid-desktop:~$ cd /home/ubuntu/intrepid-server/test-acl/
ubuntu@intrepid-desktop:~/intrepid-server/test-acl$ mkdir dir-cifs
ubuntu@intrepid-desktop:~/intrepid-server/test-acl$ touch file-cifs


I cannot use getfacl on the client to retrieve ACL on the file I just created as the cifs module in Ubuntu was not compiled with CONFIG_CIFS_XATTR.  However, if I inspect the file and directory just created on the server, here is what I get:

ubuntu@intrepid-server:/srv/share$ getfacl test-acl/*-cifs
# file: test-acl/dir-cifs
# owner: ubuntu
# group: ubuntu
user::rwx
group::r-x
other::r-x
default:user::rwx
default:group::r-x
default:other::rwx

# file: test-acl/file-cifs
# owner: ubuntu
# group: ubuntu
user::rw-
group::r--
other::r--


We can see the directory inherited the default ACL, but the file created on the client over the CIFS-mounted file system do not appear to have got the w permission propagated from the parent directory as expected.

It should be noted that setting a default ACL for a named group (ie, setfacl -m d:g:users:rwx) work just fine  with both files and directories, as expected.  It seems it is really just the default ACL for the "other" entry that do not get propagated to files.