Google maps was not installed on the latest nightly that I loaded as of 6-4-12, but even before that I couldn't update it when it was installed in earlier builds.
- The fix for me as to download and install "Maps_mod_620_cleanup_xml" from XDA (Google it and you'll find it) in recovery.
- Once you have that loaded maps will appear and will function but you will not be able to download the updates and instead get an error message when trying to do so.
- The fix from there is to use Titanium Backup Pro to make Google Maps a user app instead of a system app and reboot the TP.
- Go to the market and try to download the update again. At this point it should error out on you and prompt you to uninstall maps. Go ahead and uninstall, then reinstall it via the market.
That should leave you with a fully working version of Maps that you can actually update.
Hope this helps someone, somewhere.