Oh dear, that's an all to common sight for me. Out of the 6 people that I know that have iPhones there are only two of us (me included) still using our first bought iPhones. One person is on their 4th after only 6 months - 1 was stolen, one was dropped and shattered, and the last one was accidentally flushed down the toilet - I kid you not. We're having a sweepstake on what's going to happen the the current one.
It does seem like the lightest tap in the wrong place shatters the glass on these things.
The seemingly funny thing is that in virtually all instances of shattered iPhone screens that I've seen is that they still work. This is because the glass is not actually the touch sensor. The touch sensor is attached to the underside of the glass, but is not glass itself, so in most situations when the glass shatters the sensor remains intact, and the sensor actually keeps the glass shards together.