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I would assume that, in this area anyway, Google would follow w3 recommendations....
Some tips: URI's are case-sensitive, and "/robots.txt" string must be all lower-case. Blank lines are not permitted within a single record in the "robots.txt" file.
There must be exactly one "User-agent" field per record. The robot should be liberal in interpreting this field. A case-insensitive substring match of the name without version information is recommended.
[edited by: Robert_Charlton at 10:36 pm (utc) on May 20, 2009]