For those wondering about whether the iPhone's internal speakers get blocked by the case, it's not a problem. In fact, the back of the case is designed to augment the bass of the iPhone's speakers, and we had no problem playing a movie or hearing ringtones with the case on. I should also note that although the back lens on the iPhone is covered by a small piece of glass, my pictures weren't affected (as far as I could tell). And while you have to press a little harder to engage the volume up/down, ringer off, and power buttons, all the buttons worked fine with the case on.
LifeProof has had a lot of success with the case and has nabbed some sales from OtterBox, which used to be the king of the iPhone tough-case market. OtterBox recently announced its own waterproof iPhone 4 and 4S case, the Armor Series. At the time of this writing, that model hadn't shipped yet, but I've seen an early sample of the series, and it, too, seems like an impressive case, though it's a little bigger and heavier than the LifeProof.
In the spring of this year, LifeProof launched a line of accessories, including various mounts, an athletic armband, even a LifeJacket floaty, that are all designed to fit the case. It also announced that the case will come in additional colors.
Except for that issue with the headphone jack, this is a really a great case that should be on your shortlist if you're looking for an ultraprotective cover for your iPhone 4 or 4S. The only other downside is the price: it's expensive at $79.99 list. But if you're someone who treats your phone roughly or has a tendency to drop it, the LifeProof may be the next best thing to paying for insurance for your iPhone.