I was having a problem going from max7 obj export to zbrush last night and managed to fix the problem so I thought I'd say it here just in case anyone else had the same problem:
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In the OBJ Export box make sure "Compress Numbers" and "Relative Vertex Numbers" are <font color="yellow">UNCHECKED</font>. I also upped the # box to 10 (default is 6) if you want to preserve UVs.
http://www.cgtalk.com/showthread.php?t=184791
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