I've noticed a few mistakes in my PCB design already. Fortunately, these can be corrected manually.
Pins 2 and 6 of the MAX232 are not connected properly. This is because the Sparkfun tutorial I followed was wrong also. Looking at the datasheet for the MAX232 (and clones) you can see the right way.
I think that the MAX232 may be an optional component. It may be possible to wire the RX and TX pins of the AVR directly to the DB9. This is non-standard but may still work depending on the serial port at the other end.
The ground for the LM7805 isn't hooked to anything.
Jumper a small wire to the 9V plug's ground. Shouldn't be a big deal.
I'll log more mistakes as I find them.