I've been using KVM lately. It is essentially a version of Qemu that can take use features of modern CPUs to make the emulation go faster.
Occasionally I've had trouble with KVM/Qemu turning caps lock on and then ignoring any further presses of the caps lock key. As you can imagine, this is annoying.
The workaround: switch to the control console (control-alt-F2), then give the
sendkey caps_lock. This works.
I had to look up the name Qemu uses for the caps lock key by grepping the source code.