I posted some measurements/coordinates derived from the latest "reference" CAD files here: http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1262503015/4#4
(actually, I don't see a big reason to not duplicate the info here, so...)
Can someone point me to documentation that gives me the physical dimensions and locations of connectors, holes etc?
Welcome to "open source", where you're expected to look at the source code (EAGLE CAD files in this case) rather than rely on secondary generated documentation like dimensioned drawings. Hmm.
My concern is highlighted in particluar regarding the pin 7 8 spacing. I have downloaded Ladyada's Protoshield and found this dimension to be 155mil rather than 160mil.
Using the duemilanove reference design, I get a 2100x2700 mil bounding box with holes at (600, 2000), (2600, 1400), and (2600, 300), and the connectors at (1290, 2000), (2150, 2000), (2250, 100), and (1550, 100) (ISP connector at "about" (2555.5, 1098); ouch!)
Note that the holes of the shield connector pads are 40mils diameter, so it's pretty likely that one could place connectors 5mils in error and no one would notice without referring to the CAD files!)