I didn't experienced folding bikes directly, but in the last summer a travel companion (which came from US with a folding bike to avoid airplanes fares) had to end its tour cause of a tire: he didn't find a replacement. And we were in Innsbruck, and then in Passau, and then in Prague.

Anyway I like these small bikes. I think they should be very useful when there is a plan of mixing cycling/train/buses/etc. in the same tour.