Linux 3.6 it’s been released, with some important features:

• Btrfs: subvolume quotas, quota groups, snapshot diff, cross-subvolume file clones
• Suspend to disk and memory at the same time
• Support for SMBv2 protocol
• TCP Fast Open (client side)
• Bufferbloat fight: TCP small queues
• Safe swap over NFS/NBD
• ext4: better quota support

Looking forward into distributions to adopt it.