I am excited by EFS but during the beta it didn't perform as well as I would have liked. I had a small Wordpress install that I wanted to make elastic in that I could have multiple web servers and all of the data was stored apart from the AMI. After testing my setup I found that latency was way too high and the performance of my site was terrible. I'm guessing it's because the amount of data was really low (100MB) and the requests were infrequent.

I ended up going with a shared volume, which works fine and performance is great, but I can only attach the volume to a single instance at a time which prevents me from running multiple instances. That said, it looks like there has been some performance tweaks to EFS so maybe it might be better this time.