That thread mentions two specific rides... both of which sometimes back the FP line up out the door even in slower seasons. TT especially. We were there in March last year, not spring break, not Mardi Gras, not the weeks around Easter, just that slow bit in very early March, and the FP return line was to the doors. That's just how it is because of the way they merge and load the design rooms. But to see that kind of line at BTMRR or Splash or Space? That's unheard of, no matter how much the FP+ cheerleaders would like to pretend otherwise.
A friend (and experienced Disney traveler, DVC owner, passholder) is down there this week and has posted some very, very negative things on FB, including a 40min FP+ line; interestingly, she mentioned that part of the problem was people seeing that long line and getting in it, thinking it was standby, so the CMs at the first checkpoint had to explain that it was the FP return, and sometimes what FP+ is and how to get them, to confused guests. I'm very interested to hear her take when I see her later this week because she's been relentlessly positive about FP+ and was just there in the fall so this isn't her first go-round with the new system.