The only time I ever had problems running multiple VMs at once was when I used two different VMMs to do so. In fact, testing IE on Windows is equally painful as

The only time I ever had problems running multiple VMs at once was when I used two different VMMs to do so. In fact, testing IE on Windows is equally painful as you need the VMs for the older versions anyway (unless you happen to have a few real machines lying around). Depending on your site's demographics you may choose to ignore IE testing, I understand. But often that demographic is rather disconnected from your own development OS so you may not always get around it. Also your comment history is very JS-focused (but how does that matter in any way?).