I've had great success with planting trees that were grown in Rootmaker bags. The first time I received a shipment of Nuttall Oaks, I was quite alarmed. The trees were 2.5" caliper, yet the rootballs were merely 18" wide by 15" deep. I thought "No way do these trees have a chance!" Because of the small rootball size, they were a snap to place. And I had no trouble removing the grow bags. After we had the tree placed, we simply cut four or five vertical slits starting at the top and ripped down. It was not much harder than removing a pot with one small root growing through a drain hole. And all of these trees have performed extremely well. They have required little supplemental water and have grown considerably. I would not hesitate to purchase bag grown trees again.
Oh, and like VoodoChile said, check out Carl Whitcomb and his Rootmaker system. It is well explained on
http://www.rootmaker.com/whitsys.php