There are a few locations at DTD, such as Ghirardelli and Wetzels Pretzels, that will not accept the dining plan. Not sure if these count as CS or snack outlets.
No restaurant at the Swan and Dolphin or Shades of Green will accept the plan.
The Boardwalk To Go kiosk does not accept the plan, although Boardwalk Joe's kiosk will accept snack credits for some items.
Tutto Gusto in Epcot does not accept the plan, nor will the pub/bar at Rose & Crown, but these are considered bars/lounges and not counter service restaurants. You can order fish & chips from the outside kiosk and pay for them with a CS credit, but you can't order fish & chips from the pub and use credits as payment. (This refers to the pub area with the bar only - not the restaurant)