what does the ‘+’ mean at the end of an ls entry?

For Linux and the mac, it means that the file has an ACL associated with the file.

~% ls -ld .
drwx--x--x 163 pshanahan pshanahan 12288 2008-06-16 16:26 .
~% setfacl -m user:postfix:rx .
~% ls -ld .
drwxr-x--x+ 163 pshanahan pshanahan 12288 2008-06-16 16:26 .

On the Mac if you see an ‘@’ sign where the plus(+) is, then it indicates that there’s extended attribute information. If you’ve got a version of ls that supports extended attributes (takes the -@ option), you should see the same thing in Linux.