GPO based doesn't run in a user context and isn't really recommended - user profile is the way to go - fastest, too.

Your Use syntax doesn't look right - try this:
 Code:
$Map = '\\My Server\Users\' + @USERID
Use P: $Map /PERSISTENT
You have too many quotes in your example. Also - you should not place variables or macros inside of strings - leads to many problems.

Glenn
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Actually I am a Rocket Scientist! \:D