I have a 2011 Macbook Pro and initial versions of VIRB Edit were fine.
I have noticed in more recent versions of VIRB Edit the video will be jerky when playing back in VIRB Edit. I think they have changed some of the video libraries in VIRB Edit and it now might need a newer faster mac to keep up :(
When video is exported it is fine (so it is just while you are viewing / editing in VIRB Edit).