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Limitations
umask - ACLs are only applied generally only during create. More specifically, create(), mkdir(), mknod(), mkfifo(), or open(). Other operations will be limited by what the umask of the user performing the operation such as copy or move. (I need to go into more detail here but this is very very limiting and intuitively not the behaviour most people expect). In other words, you apply an ACL to a directory and subdirectory expecting files copied in would inherit those ACLs, well they don't because of the default umask.
Copying Files - This is no-longer an issue with modern (2012 is when I checked) versions of Ubuntu and I would guess other *nix systems. If you want to preserve specific ACL permissions and not inherit, use -p. With an older system, check that when setting default ACLs on a directory, the following commands will inherit permissions properly: local copy, sftp remote create and sftp remote copy.
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