This new version brings a lot of new and really cool stuff to the table:
WORM (write once read many) Operating version for glusterd Block device translator Duplicate Request Cache Server Quorum libgfapi VM image storage improvements – not related to QEMU integration; related to performance improvements NFSv3 ACL supportThe new QEMU integration should massively increase performance when used as backing storage for KVM virtual machines. Really nice!
More info on the project's blog: http://www.gluster.org/2013/02/new-release-glusterfs-3-4alpha/