F3 is something like this: TE CONNECTIVITY / RAYCHEM - MINISMDC075F/24 - POLYSWITCH, SMD, 1812, 0.75A
The product information from farnell says: Initial Resistance Max: 0.29 ohm / Initial Resistance Min: 0.09 ohm
The datasheet for the polypfuse F3: http://de.farnell.com/te-connectivity-r ... /1345924RL
PDF --> http://www.te.com/commerce/DocumentDeli ... RF0323-000
There (page 7) I found for 'miniSMDC075F': Rmin: 0.11 Ohm; Rmax: 0.45 Ohm
Asuming the Pi itself draws a average current of 0.5 A: results in a voltage drop between 0.06 V and 0.23 V for a 'good' fuse.
Due to limited accuracy and resolution of many cheap multimeters i would say 'from 0.1V to 0.3V drop over F3'.
I didn't find anything about the typical reset time.