We were at the Magic Kingdom during the last week of May and the FP+ kiosk lines were fine. You might wait five minutes at the kiosk immediately outside the Jungle Cruise ride, for example. I imagine this will get longer as the park grows more crowded; also, it depends on which kiosk you are accessing.
The kiosks inside City Hall, for example (which is where you would go to get a DAS card), are not busy at all, mostly because I don't think a lot of people realize that there ARE FP+ kiosks in there.