In civil 3D 2011, the point locking is supposed to lock points and protect them from edits and overwrites (according to the help file). Currently it protects from editing, but if someone chooses to overwrite locked points in a situation where duplicate points exist, the points are automatically unlocked and overwritten. In the past (LDD), unlocked points would get overwritten but locked points would get left alone.
This is something I would like to see be fixed. Ideally a hotfix for 2011, but even in future release would be a plus.
Have you tried using the survey database? When a point is imported it asks if you want to overwrite or ignore the point. Ignoring keeps the point that already exists in the drawing, but both are kept in the database under their respective import events (I think).