I know it's early to ask this, but does anyone know if figs in pots grow roots during dormancy?  Just thinking ahead and wondering if figs should be up potted in the fall if the roots are filling the smaller pot.  My figs get stored at about 40F for the winter.

I would say no.  If they do its not much, not like summer.  You can up pot at any time, so if the roots are filling that smaller pot in August, you can give them more room to grow before winter.

If the temps in the root zone stays above 50-55F the roots should continue to grow.

Hi gregmartin,
IMO, no, roots don't grow the whole winter - I was wondering the same last year, and did a test .
But, roots will start to grow let's say one month before the buds do break - This is the time when I start the fertilizing program on my figtrees.
So if you want your tree to grow stronger next Spring, pot up in the Fall. Just don't raise the temps, for instance by keeping the tree in a greenhouse, or the
tree might get tricked into making new growth in the Fall.

I can't say for certain for figs, but I do know trees will continue grow roots while they are 'dormant' in the winter.

At the garden center I work at we put our potted trees in mulch bins and cover them with 4-6" of mulch for some winter insulation. Some trees grow roots out of the pots between late November and early March. Granted, the mulch can be a bit warm from microbe activity.

I personally wouldn't up pot anything expecting winter root growth, regardless of species.

I tried keeping root pieces in the refrigerator during the winter and they did not grow rootlets until I took them out and put them in the warmth. 
Below is a copy of a post I had made some time back. It shows proof of what warmth can do to fig roots. These roots went from my fridge to the top of my hot water heater tank.


 I had put a piece of root in my cutting propagation  box and left it in for five weeks and it put on 4 1/2 inches of new root growth without even being attached to a plant. Whereas the other pieces of severed roots that were kept in the refrigerator crisper for about 4 months have not even woken up yet. 

 I find it amazing that roots can stay alive for so long and can continue to grow.
 
 Below are 2 pictures of the still growing root and one of the dormant refrigerated roots.

Attached Images
      

Thanks all, I appreciate all the great input.

Greg, even if there is no root growth during most of the winter there may be a slight advantage to up-potting in the fall, if you have the time and space to do it.  If there is in fact root growth before bud break, then you're giving the tree a slightly earlier start in the rooting process.  I don't really see any major disadvantage to doing it in the fall.