A recent study in Finland concludes: "It seems that sleep deprivation after DST transition is not harmful enough to impact on occupational accident rates."
On the other hand others report, "The real issue, however is not the later hours or extra sunlight. Studies have shown that changing the clocks is responsible for health problems (including increased heart attack and vehicular accident risks) and leads to hundreds of thousands of hours of lost productivity in workplaces across the country. Also: It's really annoying."
See also: A Whitehouse Petition to "Eliminate the bi-annual time change caused by Daylight Savings Time