Version 1.0.0 of the Virtual Machine Manager adds snapshot support for easily snapshotting a VM from the UI and putting the capability on par with the proprietary virtualization software, a new virt-xml tool, improved defaults for QCOW2 / USB 2 / Host CPU model / other features, new introspect command line options, support for ARM Versatile Express VM creation, support in the virt-manager for memory usage graphs, an UI for editing devices, SPICE USB redirection support, new command-line support, new command-line options, improved application responsiveness for remote host connections, and many UI clean-ups and other improvements.
Virt-manager has already been a decent open-source solution for managing Linux KVM and Xen guest virtual machines but now with version 1.0.0 it's a whole lot better. The snapshot support from the GUI has long been sought after by virt-manager users, improved defaults are always good, SPICE USB redirection, and other capabilities make virt-manager 1.0.0 an excellent Valentine's Day present. The virt-manager 1.0.0 changes are mentioned via this Git commit. There's also more 1.0 details on Cole Robinson's blog, a Red Hat employee working on the virt-manager open-source project.