Among the new features to QEMU 1.3 is support for the Linux VFIO driver that was merged into the Linux 3.6 kernel for assigning PCI devices to a virtual machine, the MIPS target now supports Loongson Multimedia Instructions and MIPS32/MIPS64 ASE DSP instructions, TCG emulation supports Intel SMEP and SMAP features of new x86 processors, support for Intel Haswell and AMD Opteron G5 processors, Xtensa single-precision floating point instruction support, USB redirection now supports live migration, improved USB 3.0 support, a new para-virtualized hardware random number generator, and various block device improvements.
The SPICE support in QEMU 1.3 now supports seamless migration, composite QXL commands, multiple monitor support on a single PCI device, arbitrary resolution support, and various other display-related work. Sadly though there's still no guest 3D support for this common Linux virtualization setup. When it comes to KVM, QEMU now supports old-style PCI device assignment as found in the earlier qemu-kvm work. Some of the other QEMU 1.3 features were detailed in a Phoronix article last month.
More information on QEMU 1.3 features can be found from the QEMU Wiki.