I've used a Sharksaw Dowel saw (http://www.diy.com/diy/jsp/bq/product/product.jsp?CATID=62656&entryFlag=false&PR...) when trimming a door for laminate or carpets. Though I've only used it on new doors where it works quite well. Nice and bendy when using a spare bit of laminate laid on the underlay as a guide and rest. On old doors I take the door off and use an electric plane and/or a circular saw. Not come across an occasion where nails or screws are in the door at the bottom, though I've only trimmed 20 odd doors up till now.