I uploaded my latest revision to a shared folder
[new uload 1/22].
As Trialex suggested, I added a 3.3v regulator (mcp1700-330) and caps, and also made the jumper pads/vias and their holes bigger. Along the way I also noticed that I hadn't routed the input power to the "Vin" or "9V" pin, so that's fixed too.
I tried different main chip orientations, and followed westfw's example of rotating it 45 degrees-- gave plenty of room for power regulation in the lower left.
I'm not too happy with the power jumpers under the chip socket, but it should work OK and not be too tough to build out. And there are still more jumpers than I'd like, but since not everyone will need the ICSP (or is it just ISP?) header, it might not a big deal.
I'm curious if anybody would mind looking over the schematic for any errors or glaring omissions? I'll breadboard it in the coming week and try to get a sketch uploaded, but would appreciate any tips!
* (almost) everything optional,
* barrel jack, .1" pin headers, or screw terminals for power input,
* solder jumpers to bypass the diode and voltage regulator,
* pin jumper to bypass the voltage regulator,
* fourth standoff mounting hole for stability,
* grounded hole for mounting a resonator instead of a crystal and caps.
All suggestions welcome!