When I tiller a bow, I've always just centered the bow on the tree, but when doing some reading I noticed that some people shift the bow in one direction, I assume to put the arrow shelf in the center of the tree.  Perhaps this is done on a bow with a shorter bottom limb where the shelf actually falls closer to center.  That part I'm not sure of.
Anyway, on a bow with equal length limbs, should I be shifting the bow to the side and centering the arrow shelf on the tree, or is the way I've been doing it ok?

I used to tiller a bow with the center of the bow on the tree, and found the tiller to be off just a tad. To see it tho you have to draw the bow with the bow on a pivot point. I use a half round piece of wood I can put on the shelf of the tree toward final tiller. This simulates how the bow will be draw a whole lot closer. I think Dean Torges calls this dynamic balance. Try it you'll like it.  

Ok, I understand how that would work, but how do you center the handle/bow on the tiller tree, off a little to the side or perfectly centered?

You don't center the handle, you pivot the bow where you would normally draw it from, lets say 1 1/4" above center. I'm sure someone will come on here that can explain it better than I.

dano,
you dont use the whole handle, only the point where your hand pushes? am i right? in germany we say "druckpunkt". i dont know in english. perhaps "point of pressure"?

I think what everone is saying is you place it on the handle as if it where your hand

That being the case, you would center where the handle is cut in (the low point)as that is where all the pressure rests.  When making the handle, I've always tried to make that the center point anyway.
But on an osage self bow for example, there is likely no such cut in spot.

Checking tiller on a tiller tree and again in your hand will be somewhat different. The tree is static and your hand will compensate for slight inequities. I do all of my tillering with a tree. I don't measure for positive or negative tiller. When I look at my hand held tiller it generally looks right to me. Sometimes, after shooting a few arrows I will readjust the tiller a bit.

This may be a dumb question, but how does one go about checking hand held tiller?

you can check it with a mirror, or with a friend who draws the bow.

Or with a camera with a self timer or a video camera. Or have someone take a picture of you pulling the bow and then post it here

I work from the center. I also draw the bow in my hand, in front of a mirror and in front of a digicam held by my wife. Jawge

I'm deffinitely no expert but I tiller on the tree with the center of the handle positioned on the center of the tree shelf. I also have my wife take a picture of me at full draw.