Just to lend a hand and put a little water on the fire.  This is a convo I had with Baritus on cryptsy. The subject is a faster difficulty adjustment and why he decided that was a risky option.  He said the problem comes down to variability and he explains it like this:

baritus320: Variance is the potential random variability in the computing power of the network. In the extreme example of 1 block retarget variance: One guy gets lucky and mines the block in 1 second under 1 difficulty, the next guy also gets lucky but now the difficulty is 3, so it goes to 30. network = struck.  The more blocks, the less the chance of something like that happening due to variance.