According the Wiki and other threads on this forum, the RPi has 3 fuses.
F1 and F2 are on side of USB ports, with 140mA limit (each USB port).
F3 is near the micro USB plug (on opposite side), and is 750mA limited.
And EXIST's a 5V GPIO. P1 on GPIO connector is 3V3. The pin on other row is 5V. Find it on the Wiki.
So, since RPi can consume 700mA on full load with USB loads, there's no much current to 5V GPIO.
If you don't use USB devices on RPi (use devices on powered USB hub instead), you can have 200~300 mA on 5V GPIO.
There people putting 5V directly on 5V GPIO instead of micro USB plug. You will lose the F3 fuse protection in case of short circuit.
#HARDWARE MOD, WARRANTY VOID!#
Or you can just make a bridge (with wire) over the F3 fuse and keep using the micro USB plug to power the entire board.
To avoid the current limit on USB ports of RPi, is possible to solder wires on USB plug from 5V GPIO or even micro USB plug.