No, it's a diagram (which was designed before we even had betas) which is not to scale; it's to demonstrate where the ports are and what the different bits on the board do to non-technical people. (It's designed by Paul Beech, who is also behind our logo, and it's been very useful for that purpose; you may have seen it reproduced in a number of newspapers.)
If you're building cases, there are measurements that Gert has taken with some Vernier callipers at
http://www.raspberrypi.org/forum/projec ... nical-data – note that until we get production boards back these are not absolutely set in stone, because things may change in manufacture.