Passengers exiting with carry-on baggage were the most frequently cited obstruction to evacuation. Twenty-four of the 36 flight attendants who responded listed carry-on baggage as an obstruction. Overall, 37 percent of the passengers indicated that retrieving carry-on baggage slowed the evacuation; however, in five of the evacuations (cases 9, 16, 24, 27, and 32), a majority of passengers believed that the evacuation was slowed by carry-on baggage. Further, 70 passengers and 8 flight attendants reported arguments between passengers and flight attendants regarding luggage.
[...] The Safety Board concludes that passengers’ efforts to evacuate an airplane with their carry-on baggage continue to pose a problem for flight attendants and are a serious risk to a successful evacuation of an airplane. """
http://www.ntsb.gov/doclib/safetystudies/SS0001.pdf (page 66-68)