Line6man, if I may interject with two questions.
1) What does the optional 0.047 uF capacitor do between the switch and (what I assume to be) the bridge pickup volume?
2) How exactly does that mono plug mix the signals? For that matter, it doesn't even look like a regular mono plug, not with that rectangle connecting the hot output and the incoming signal.
M0ses already answered #1 for you.
As far as #2,
There is a break terminal on the mono jack. (Well, is it still called a break terminal if it's on the outside of the tip connector so that it connects when a cable is inserted, rather than connecting when a cable is removed?)
When you plug a cable into the jack, the physical motion of the tip terminal in the jack pushing outward causes the break terminal to make contact with the tip terminal, which connects the second pickup to the jack.
Personally, I prefer a different approach to mono/stereo wiring.
Instead of having seperate mono and stereo outs, I would rather have two mono outputs with break terminals that disconnect when a cable is inserted. If you wire the tip terminal on the first jack into the break on the second, and the tip terminal on the second jack into the break on the first, you can have it so that when you plug a cable into only one jack, (Either jack, it does not matter.) you have a mono output, but when cables are plugged into both jacks, you have a stereo output.
I guess it's personal preference though, depending on if you like both signals in one cable for stereo, or two separate cables.