- New controversial filesystem structure changes (/lib/, /lib64/, /bin/, and /sbin/ directories have been removed and are now under /usr/)
- EXT4 now support filesystems larger than 16TB
- Removable disks are no longer mounted under /media/, but instead under/run/media/$USER/
- Linux 3.3.4
- Better power support for Sandy Bridge
- Updated KVM version
- New sandbox feature that allows applications to be isolated.
- KVM management client (virt-manager) now supports USB-passthrough to attach things like USB external hard drives to virtual machines.
- Multilayer virtual switch (Open vSwitch)
- Better disk emulation
You can also read more about the changes in Fedora 17 at this great H-Online article.