The Linux 3.7 kernel is already looking quite significant and the EXT4 file-system updates for this next kernel release don't appear to disappoint. As outlined in the Git pull, there's improvements to online resizing and fixes for a number of races, some of which could have led to deadlocks with the EXT4 a-synchronous I/O and online defragmentation support. There's also various other minor bug-fixes and code clean-ups.
The online resizing improvements for EXT4 in Linux allow for resizing file-systems that are greater than 16 Terabytes in size by using the meta_bg feature. The speed of online resizing has also been accelerated regardless of file-system size.