I'm looking at the EAGLE board file from the Arduino wiki page, and I feel like I must be missing something - none of the ground pins of U1 appear to be connected to anything:
As you can see, the GND pin on the bottom right is unconnected, as is the GND at pin 5. The GND at pin 3 is connected to a via which goes... nowhere?
Here's the board file with just the top layer showing, for further clarity:
For more weirdness, you can see here that there's a weird trace going off to nowhere from the ground side of the upper decoupling cap.
Admittedly I'm not used to using EAGLE, so I tried the brute-force approach of enabling every single layer in case I was missing an obscurely named inner layer or ground pour, but as far as I can tell there's no connection at all.
What am I missing? Is the board file missing stuff, or have I got something hidden?