First and foremost, it appears you are in violation of the National Electric Code (NFPA 70). No worries, it's an easy fix AND it's for your own safety!! To be compliant with the code you will need to ground your "vehicle ground rod" to your home grounding network as all the grounds must be at the same ground potential. An easy solution is to run a #12 green insulated cable from your "vehicle ground rod" to the nearest receptacle in your garage and splice into the grounding connection on that receptacle.
Your concern with your computer blowing up isn't without warrant but it should be fine if lighting strikes (assuming you've complied with the code). The chances of your computer frying from lighting are about the same as from frying because of driving. Assuming you tied your "vehicle ground rod" to your home grounding system by the time lighting hit your home, there would be no voltage potential difference between your home and your car thus not causing any type of arcing resulting in damage to either your home, vehicle, or you. If that happened with you in the garage chances are the arc would take the path of least resistance, you.
This trick can actually work to some degree, but only in areas where there isn't much humidity. Our cars build up static charge just from driving around and our tires (rubber is an insulator) don't allow it to dissipate easily, however humidity in the air does.
As far as I can tell, you shouldn't have any problems with metal corrision.
