Offset is 4/10 of a pin and it really hinders cheeep and easy hacking. Great idea but too late now, its the de facto standard for Arduinos and shields. Various workarounds:
http://brettbeauregard.com/blog/2009/07/arduino-offset-header/
http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1247778571
http://www.coolcomponents.co.uk/catalog/product_info.php?products_id=374
http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1240862639