I noticed that on both Windows XP and 7 (and 2 different computers respectively) I could manage to get that "This device can perform faster if you connect it to a high-speed USB 2.0 port" notification to pop up if I connect the cable very slowly (or struggle a bit doing it with just one hand). If I connect it quickly enough or normally, with both hands, there is no notification. In either case, all such devices appear to function normally.
What I think happens is that the contact between wires gets interrupted for enough time during slow/clumsy connection that the USB controller thinks it's not 2.0 but slower. But why does it think so? Or why does it not just say "You are bad at connecting cables, please unplug and try again"?