The Fedora Engineering Steering Committee (FESCo) has approved the Fedora 16 Btrfs default file-system feature, which would change the default Linux file-system on new installations from being EXT4 to Btrfs. Existing Fedora installations being upgraded would go unchanged.
The Btrfs volume management capabilities would be taken advantage of instead of using LVM as is the case now. There's also snapshots, check-summing, transparent Zlib/LZO compression, and other features to take advantage of with this Oracle-sponsored solution. Fedora can already take advantage of Btrfs snapshots to do system roll-backs.
If things don't go as planned, however, Fedora 16 could end up using EXT4 as the default and postpone this switch until Fedora 17. The Fedora 16 release is planned for late October or early November.