OS X 10.9 (Mavericks) brings SMB 2 as the default network protocol - with OS X 10.10 (Yosemite) SMB 3 has been added. If you face issues connecting to your NAS or connections to Windows file servers don't work as expected (e.g. inability to rename files or folders) it may help to switch back to the slower but more reliable SMB 1.
What is new in this release:
Added: Compatibility with OS X 10.11 (El Capitan)