Just upgraded to 10 from 9 (as part of the August upgrade program) and I've noticed a little niggle regarding the mouse. The machine appears speedy enough with regard to responsiveness of boot/programs/typing. However, when I move the mouse, (the speed is perfect and responsive) theres a lag between the mouse moving over things/dragging a window/ click'n'drag highlights/ and them lighting up and moving, its like they are in slow motion and a few ms behind the input. I have tried all the mouse options in the configure pane (things like smooth mouse produces crazy behaviour) to no avail. As I say, the muse speed is perfect, its just the context behaviours it seems to lag on. On the Windows side its set up with 3 CPUs / 8000MB RAM / 1024MB VRAM / Win8.1 On the Mac side its 10.9.4 Mac is a New Mac Pro 6-Core / 16GB / D700 FirePros / Cyborg R.A.T 7 Contagion USB Mouse Now, when i change to an old Microsoft USB Mouse (intelimouse optical: the original circa ~yr2000) the mouse speed obviously decreases but so does the lag in the VM. I'm used to turbo speeds (i have the RAT at around 2500DPi) but in Parallels 9, the lag wasn't present on the RAT! Has something changed in the way it handles the mouse?