First: the parts:
On the parts list check, http://www.ladyada.net/make/usbtinyisp/parts.html
you suggested digikey part 151-1081-ND ; I found out the hard and frustrating way that that connector is actually complete [EDIT]. The through-hole pins are very slim, and bend easily. This in combination with there being a rear aluminum cover causes problems.
The pins are in such close proximity to the rear cover that it doesn't take much to end up shorting those two rear pins to the rear of the case. This was very frustrating; it wasn't until I plugged just the connector itself in to a non-stupid-sony-vaio-laptop that dmesg started telling me about how the port was being shut down because there was too much current. With nothing attached to the pins, I became enlightened to the fact that the connector itself was becoming shorted.
I heavily suggest, from experience, that the parts list be changed to suggest digikey part A31725-ND ; much sturdier, no stupid rear-cover to short out the leads, identical footprint, and very much worth the extra $0.66.
You then suggest a 12MHz resonator. This turned out to be more problematic than I anticipated. I actually constructed my usbtiny on a breadboard (I didn't want to buy your PCB and I liked the idea of doing raw usb signaling on a breadboard).
The main trouble with breadboarding a resonator is unlike a crystal, because the two XTAL pins aren't adjacent, you can't just shove it directly on the breadboard and then pop on the two caps. This actually caused more problems than I anticipated. I stuck the in front of the 2313 on the board, and jumpered it to the xtal pins. This then later got in the way of my original breadboard routing plan, so I then put it on the opposite side of the breadboard, and used two more jumpers (meaning triple the capacitance between the 2313 and the resonator in comparison to a crystal).
This extra capacitance actually ended up causing funky timing problems (writes and reads would fail inconsistently), that I eventually solved by rerouting things back over to the other side of the breadboard, and only using a single pair of jumpers.
I suggest replacing the resonator with a crystal and two caps. Of course this would require a different board layout, but I don't think overall cost should increase that much. Had I thought for a moment and not followed the schematic so blindly, I think my frustration level would have been reduced dramatically.
Finally there's also an error on the schematic, http://www.ladyada.net/images/usbtinyis ... sp2sch.png
. You have pin 11 and 12 swapped on the symbol for IC2D--that is, the symbol itself is flipped, but the actual pin assignments are correct. This also caused some amount of confusion when I was comparing the 74AHC125 datasheet to what you had written on the schematic.
Here's what I made: (attached) ; the USB connector pictured is actually a vertical connector that I also used that seemed to work the best on the breadboard with the copper wire soldered on (least mechanical stress). It's targeting a mega1284p. After dealing with several problems with the capacitance of the breadboard nodes, along with the other things I mentioned, it works surprisingly very well.
The other changes I made were using a ferrite bead to help reduce noise on Vcc, and a zener diode pulling the reset pin high, both of which are the recommended/optimal ways to do this according to Atmel: http://www.atmel.com/images/doc2521.pdf