“Using existing data that shows that people exhibit poorer self-control when they're tired, the researchers said that the lost sleep due to the time change -- an average of 40 minutes that Sunday night -- makes employees less likely to self-regulate their behavior and more inclined to spend time cyberloafing, or surfing the Internet for personal pursuits while on the clock,” according to a Penn State report on the research.
The article also attributes some lost productivity to DST coinciding with March Madness, however I will focus only on the time change. Just to provide some anecdotal evidence of my own, I witnessed 3 co-workers chatting instead of working for at least 30 minutes. While it's entirely possible this has nothing to do with DST, it's at least coincidental.
I've got a reasonable proposal. If we absolutely must change our clocks twice a year (and I see no reason why we should) instead of shocking everyone with the hour change, why not ease into it by changing 10 minutes a day for 6 days. That would be much easier to adjust to. Otherwise I have to start looking at jobs in Arizona or one of the other states that doesn't recognize DST.