Update on reception:
I spent the day driving around LA today running errands. I was fairly certain that my reception was worse than usual (previous case was a plastic/rubber bumper) until I decided to go into the Apple store at the Grove and do a side by side signal strength test with one of their display models.
I placed both my Jett iphone and the display iphone flat on the table separated by about an inch and put each into field test mode. I was surprised to say the least to see that the signal strength on my iphone was actually slightly better than the bare display iphone - my signal strength was bouncing between -103 and -105 while the display iphone's signal strength was bouncing between -108 and -111. At one point, the display iphone actually lost its signal altogether and went in to search mode while my iphone still held its signal.
Now obviously there are a ton of variables that could have impacted the results of my impromptu test, and ideally I would have like to have run the test again, but with the Jett on the display iphone and with my iphone being bare, but that wasn't really an option for obvious reasons. But at the very least it suggests that the Jett case wasn't making my iphone perform worse than the display iphone.
On the other hand, I would swear that my reception in my house has been a little worse with the Jett based on the number of bars I get (I don't make a habit of keeping my iphone in field test mode at home). Pre-Jett, I would typically get 2 bars at home, sometimes 3, and now I seem to be bouncing back and forth between 1 and 2 bars, and never 3. Also, for the first time EVER with my iphone 4, I had someone complain today about the connection being bad while using my iphone at home.
So, Apple store test notwithstanding, jury is still out for me on reception.