A long time ago, Steve wrote a post about setting up abuse and postmaster addresses for Google hosted domains. Google has gone through a couple iterations of the interface since then, as you can see by the comment stream.
I checked with some people who have Google hosted domains and they have confirmed that abuse@ and postmaster@ addresses can be set up by creating a group. When you create the group you can then add yourself to the group and get the mail that comes into abuse@ and postmaster@.
Gmail abuse and postmaster addresses
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