Originally Posted by
eschlwc
... so let's say there's more space between drive-side locknut and table compared to the nds. which side do i tighten?
...
Tighten the side with more space, loosen the side with less space.
edit: Doh! no, as jab points out (see below) I got that wrong. Tighten the side with less space. 
Originally Posted by
eschlwc
if the difference is 4mm (meaning an error of 2mm), do you try to true this slight error away?
Yes, unless I was feeling very lazy (which is not unprecedented). Bear in mind that you may be able to correct the error by moving a 2 mm washer from one side of the axle to the other.
Originally Posted by
eschlwc
how much does it normally take to move a rim 2mm to one side? a half turn on each spoke on that side?
surprisingly little, but I don't remember.
Originally Posted by
eschlwc
what's a reasonable length in dishing error to leave in place?
That's a judgment call I'm going to leave in your hands. There comes a point in a long ride when I just want to sit up straight and stretch my arms out to both sides and try to relax my neck muscles for a little while, while let the bike steer itself. At this point, I like to see the front wheel perfectly centered in front of me. If I see more of one side of the wheel than the other, and have to compensate by putting a kink in my spine, I can't relax my neck; and I know i didn't dish the wheels properly.