We either do Epcot or MK on the first day. If we're staying @ the Beach Club, we pick up the
DAS at the rear entrance of Epcot at the "regular" kiosk. If we go to MK first, we head straight to Guest Relations and take care of it first thing after park opening. Lasts for the duration of our trip, and, tied in with our Fast Passes, we have little problems negotiating the parks. In fact, our last trip, we picked up the DAS @ Epcot, had our ADR @ MK the next day (first in line for Cinderella's Castle b/c more people went to the newer "Be Our Guest" breakfast), then waited only 10 minutes in line for Elsa and Anna after breakfast. Typically, we plan our ADR subsequent to getting the DAS, so I can't speak to personal experience with the last part. However, guest relations are only open during normal park operating hours, so you may have to go back.