It's been about 4 weeks since I bought my NikeFree's. At first I didn't experience any leg fatigue or pain. I've done a long (ish) run, a bunch of 5k length runs, and even a 5k race.
I have slight shin pain (chronic issue) not as bad as I would think though, and it's not constant. Otherwise nothing! :)
I was definitely thinking it would be a rougher transition to a piece of running footwear that didn't have a lot of support. It seems it's going pretty smoothly so far!
Gotta get out there for a run...