Simics and other simulation solutions are a great way to add more variation to your software testing. I have just documented a nice case of this on my blog at the Intel Developer Zone (IDZ), where the Simics team found a bug in how Xen deals with MPX instructions when using VT-x. Thanks to running on Simics, where scenarios not available in current hardware are easy to set up.
Programming note: my Software Evangelist blog at Intel has also moved into the IDZ, and thus there is a new page where you can find all my Intel-hosted blogs. This page is found at https://software.intel.com/en-us/meet-the-developers/evangelists/team/jakob-engblom