Initial setup very clear, straightforward. I tested it by pressing the 28-pin socket into place, then soldered a ZIF socket into place. Nothing to comment on the instructions. Despite my Vulcan-sounding criticism, you have a great product. Keep up the good work!
I purchased it to revive two apparently dead 328p-pu chips. Neither can be placed into programming mode by a standard ISP board, both read 3 for the built in fuses by your board, and neither will accept a sketch on two different Uno boards, although the error for each is different. I will post more information under a different thread. My feedback here:
When placing the board on an Arduino (mega, at least), it's possible to mount the board backwards. I recommend adding some silkscreened pin identifiers (A0-5, GND, 5v, VIN, D0-13, etc.) to assist in placement.
Make even LOUDER notifications the socket must be empty when loading the sketch and running the sketch. I tried to load the sketch a few times before suspecting the socket needed to be empty and then finding the notification.
It's not altogether clear if the board is used to do anything other than set the 2 or 3 relevant fuses, I found it when I came across one or more articles saying that if you've disabled the internal clock on your 328, a high-voltage programmer is one of the few ways to re-enable it and bring the chip back from the dead.
Also, even with the comments in the sketch it's unclear if the functionality on this is different on an Arduino Mega vs a standard Arduino. I happened to have a Mega lying around so I've simply avoided the issue by using it and by using a Mega.
You don't include instructions on how to use HVSP as referenced on line 13 of your code revision 3/15/11 2.12 (assuming that's a code revision and not a board revision number). I recommend adding a sketch version number near the top line of the code. If the board supports HVSP but this sketch does not, you should state so on line 13.