Depends on the cause of the deflation. Deflation due to a collapse in aggregate demand is bad. Deflation due to an increase in aggregate supply is good, at least in a healthy economic system. Any deflation is bad in the current system because there's way too much debt.
This sums it up better for me than the countless numbers of posts on this topic. A little monetary deflation is just the opposite of a little monetary inflation. Nothing dramatic.
I would really like people to finally put the non-argument of people postponing purchasing of goods due to falling prices to rest. No one has unlimited time on this planet so no one is going to walk for another year (and then again as in perpetuity) because a car would be 2% cheaper the next year.
We deserve better thinking.