Hi Denny,
If you're starting with cuttings or seedlings, you'd probably want to lift them the first year to prune back the tap root and get a good radial root system going.
After that point, I would say that every other year or every third year would be about right during the developmental stage. If you lift every year you can't take advantage of the stored reserves and growth that the established root systems provide. They basically explode once established, so don't stand too close come spring!
In Bonsai Today Magazine, one of the field growers would just leave the plant in place and cut under and along one side with a sharp shovel. East side one year, west side the next, or something like that.
You'll get as much advice as there are people to give it, but that's how I see it. You can find some more info about field growing in the
bonsaiTALK Links section under Techniques-> Developing.
Regards,
Matt