This is how I understand it. (Please keep in mind that for me, two brains would only increase the amount of conversations of the people inside my head):
 
The trim pot on the 3-way is a gain boost.  It allows adjustments of how much gain you want to add to the pickup.    
 
It?s an off/on/boost.  The off position is for just that, to turn the pup off.  I guess you could achieve the same effect by turning the gain pot down, but it does come in handy when wanting to introduce a predetermined, specific volume to into the mix quickly.
 
Mica has made it clear to me in a previous post (I think it was the one about the square blue plastic thingie?.) that this is not a Q switch.
 
Great picture Tom.

Hollis,
 
The description for the Skylark switches is Off/On/Bright, and I don't think they would put 'bright' if they meant 'boost' (http://www.alembicguitars.net/prod/skylark.html).
 
Perhaps it acts like the treble boost switch on the Europa package?

Hollis; here is the previous thread:
 
http://club.alembicguitars.net/Images/393/8187.html
 
And the quote from Mica:
 
The switches on your guitar are pickup selectors. When you're in playing position from top to bottom it's:  
 
off  
on  
bright  
 
The trimpot on the switch is the amount of brightness. Turn it clockwise to get a bigger difference between the middle and down positions.

Right you are, thanks for correcting my  terminology..... See what I mean about two brains?
 
Thanks again.