Certain places don't take ADR's at all like ESPN club and Beaches and Cream.
Others have had success at off the beaten path places like Maya Grill, Trail's End, and Olivia's.
Many of the eateries in DTD are fairly easy to walk up to, especially those not on the
DDP.
But my advice for anyone going without an ADR is call before you leave your hotel, or stop at your lobby concierge or guest services at the park. A simple phone call can save you a wasted bus ride, or a trek across a crowded park.
I have made the call at 5:30PM from the exit of the MK for a 6 PM dinner at WCC. Hopped on the boat to WL and was seated immediately. Meanwhile, walk ups were being turned away.
Others have reported similar stories where they walked up to the podium and were told "NO!".....then place a phone call and snag an ADR for 15 minutes later at the same exact restaurant.
Make use of guest service, lobby concierge and the WDW-DINE line for same day ADR's (Even same hour ADR's!)