Parallels Desktop and VMware Fusion on the same box

I need to perform virtualization tests with either Parallels Desktop and VMware Fusion and I have only one Mac box: can I install either Parallels Desktop and VMware Fusion on the same Mac box?
Is there any warning or any issue I must consider?
Given I can install both hypervisors on the same Mac box, can I use them concurrently or should I use only one at a time?
Regards
marius

 

Generally spoken with v. 3 of Fusion and v. 6 of Parallels, you can install both on the same box. But running both concurrently can show some strange effects as both use the same host hardware.