The antennagate madness seems to be finished now (everybody knows now that Apple's faulty design is causing signal lose, or even call drops), and the next problem, generically named glassgate, has just started. It was believed that it was just the creation of the competitors, but it seems to be quite real now because Apple has taken measures against this problem.
It is not clear how resistant the glass from the back of the device is, as there were reports which said that after the device has been repeatedly taken out and inserted back from and in some cases, scratches occurred on that glass. It seems that dust particles can get stuck when the cases are inserted (between the case and the glass), causing serious scratches on the glass. In fact, these scratches will, eventually, create cracks on the whole glass surface from the back of the iPhone 4.
It seems that Apple is aware of this issue, because they pulled from the Apple Stores from all around the world all cases of this type (at least until this problem is clarified). So, if you don't have a case, you'll get call drops because of the way Apple designed iPhone's antenna. But if you get one (anything else except the bumper), you risk to have the glass from the back of the device even cracked.
I already see Apple telling everybody that their products doesn't have any issues, and users are the only ones responsible for that scratches/cracks (just as they did with Antennagate).