I'm using the XNA 4 obj importer content pipeline same from AppHub, but it generates a strange "index out of array" error when it tries to built the file, starting with the f entries in the OBJ. It seems to load the v and vn vectors just fine. The code basically runs the f entries through the .NET RegEx.Split method, but it chokes on those entries.
I searched the bug database for OBJ related errors and I did read something about a problem with the character(s) used to designate a line split, perhaps .NET has a problem reading the file because of this? The logic is pretty basic and looked right to me, it choked at the beginning of the line like it couldn't even read the f entry properly.