>That's interesting - does using "Open" versus "Import" in Illustrator for PDF files do different things with organizing the PDF content?

Yes it seems so when I open the PDF directly everything is on one layer but when I import the PDF it comes in organized.


>can you test the above AI file

It is unfortunately the same mess as opening the PDF directly (Illustrator CS3) but I can select one piece of thin line then go to Select > Same > Stroke Weight and move everything to a new layer or change the stroke width for all selected lines.

A seperate PNG file is not bad because I could treat it seperately in another program e.g. convert it to line art.