I am using them with pretty good results, its only been about 3-4 months since repot. Currently, I am using them in the more drought tolerant trees like pomegranate, jujube, and citrus. I bought a batch of (10) 18 gal fabric containers from ebay for a good price (think it was $89). I am going to possibly repot Julie mango in one next month. My main worries with them were drying out to fast due to the increased aeration (I don't know if I would repot the Lychees in fabric containers). I have been trying a 5/1/1 mix of Pine bark, Perlite, and Peatmoss. The plants seem to like this mix.
Cara Cara Orange and Anna Apple in fabric containers.

I am also trying out superoots air pruning containers with a Ewais Mango, so far its going well. I will be able to tell a bigger difference in performance of the trees once the temps warm up in the spring time. I try to also raise the fabric containers off the ground with a brick, however I have not done this with all of them. Thanks Kevin for the heads up, I am going to try to finish up raising the rest of the containers off the ground.