Polyfuses are temperature driven and will reset within a few seconds. USB ports on non-cheap bare-minimum laptops use a chip in monitoring the current draw and can block that port. The OS can re-enable the port right away but I believe OS X requires you to reboot.
OS-X (Yosemite + El Capitan) has displayed the message to me: "Your device tried to draw too much current and so the USB port has been disabled".
When I took the offending cable out, and tried with a different device, it worked straight away, no reboot required (not sure about earlier versions/alternative scenarios though, it's possible they do require a reboot).
I was going by a "polyswitch fundamentals" doc from a manufacturer[1] - and had the weasel-word "properly" :)
Apparently the resistance falls quickly at first but can take a long time to fully return to pre-trip level.
This has caused trouble in the Raspberry Pi. Users were getting odd effects when voltages didn't quite return to spec after polyfuse trip. [2]
[1] http://www.te.com/content/dam/te-com/documents/circuit-prote...
AHA! Interesting.
This explains why my computer has a bunch of USB3 ports that work... sometimes. (It also very sporadically has a massive wibble and hard-crashes with an error relating to USB.)
Apparently polyfuses can take days to properly un-trip.