Maya MEL script that breaks up a mesh based on materials. Created by Andrew Coggeshall at Basenji Games.

SepScript.mel

// Poly Separate
// Copyright (C) 2012 Basenji Games
// Licensed under the MIT license

string $selection[] = `ls -sl`;
sepMat($selection[0]);

global proc sepMat(string $object){
string $shadingGroups[] = getSGsFromShape($object);
string $ParentName = ($object + "_lightMap_Group");
group -empty -n $ParentName;

	for ($i = 0; $i < size($shadingGroups) ; $i = $i + 1)
	{
		string $theMaterial[] = `listConnections -d off -s on $shadingGroups[$i]`;
		string $clone = ($object + "_" + $theMaterial[0]);
		duplicate -n $clone  $object;
		parent $clone $ParentName;
		
			string $material[] = `listConnections -d off -s on $shadingGroups[$i]`;
			select $clone; ConvertSelectionToFaces;
			string $tempset = `sets`;
			string $tempgrps[] = `listConnections -type shadingEngine $material[0]`;
			select `sets -int $tempset $tempgrps[0]`;
			
			
			InvertSelection;
			delete;
	}
	delete $object;
}



proc string[] getSGsFromShape( string $shape )
{
string $myShapeNode[] = `listRelatives -children -shapes $shape`;
  string $shadingEngines[];

  if ( `objExists $shape` )
  {
    string $dest[] = `listConnections -destination true -source false
      -plugs false -type "shadingEngine" $myShapeNode[0]`;

    if ( size( $dest ) )
    {
      string $select[] = `ls -sl`;
      select -r -ne $dest;
      $shadingEngines = `ls -sl`;
      select -r $select;
    }
  }

  return $shadingEngines;
}