Heise.de's Kernel Log has a look at the ext4 filesystem
as Linus Torvalds has integrated a large collection of patches for it into the kernel main branch. "This signals that with the next kernel version 2.6.28, the successor to ext3 will finally leave behind its 'hot' development phase." The article notes that ext4 developer Theodore Ts'o (tytso) is in favor of ultimately moving Linux to a modern, "next-generation" file system. His preferred choice is btrfs, and Heise notes an email
Ts'o sent to the Linux Kernel Mailing List a week back positioning ext4 as a bridge to btrfs.