Massive under certain use cases, and major reliability and feature differences too. A lot of BtrFS is still "in progress" like the copy-on-write stuff and fault detection.

Actually I'm using BtrFS on a few Ubuntu server 14.04 virtual machines. It's very nice when I need to add extra hard disk space, and I only need to add or expand de the virtual hard disk, and indicate to the filesystem to append the extra new space. Also, transparent compression comes very useful, on special when our applications are very dependent on I/O performance and need to store a lot of write single time/read a lot of times data.