RECEPTION UPDATE:
After a solid week of heavy use both at home in LA and on a 4 day road trip up the coast to Mendocino, I'm convinced that this case is having a significant adverse effect on my reception. Pre-JETT, I virtually never had dropped calls at my house and my IP4 consistently had better reception than my wife's 3GS. Since putting on the JETT, I've had 8-12 dropped calls at my house and on my road trip found that my IP4 often showed "NO SERVICE" while my wife's 3GS was showing 1-2 bars of service. I wouldn't say the difference between my wife's 3GS and my IP4 was huge, but her 3GS was clearly getting better reception on average during our trip, whereas it was the opposite pre-JETT.
What's baffling me is that over the first couple days I ran dozens of numerical signal strength tests using the field test mode in comparison to 3 other IP4s (one of which was a display model at an Apple store) and my wife's 3GS, and my JETT IP4 never showed any signal inferiority to the other phones. And yet my real world use over the last week clearly suggests otherwise.