From me too ... Thank you @oliverjenkins very much for this brave step and all the details.
I stumbled on this thread after suffering with the existing loose onboard USB sockets for days ... my USB device frequently loses connection when moved even a millimeter using the standard USB sockets. Cross-checking with other sockets on other PCs it seems most USB sockets exhibit this loosness BUT without losing connection.
So with this mod I can locate my USB device anywhere and not worry about connection to the RPi.
If it's any help, de-soldering a tricky item may be helped by heating in stages using heat-resistant wedges, no de-soldering tools required.
Start with a thin (blunt!) razor blade wedged gently but firmly between the 'board and the connector.
Add heat to all the solder points - the connector will disengage slightly. Add heat to all the solder points again.
Move the thin (blunt!) razor blade gently but firmly towards the center of the board.
Add heat to all the solder points - the connector will again disengage slightly. Add heat to all the solder points again.
Repeat until the job is done. (You may need to add more THIN wedges as you go.)
Then it's time for the de-soldering tools (I prefer wicks rather than vacuum pumps but it's a personal preference.)
Again, thanks @oliverjenkins for taking the lead on this.
PS as the RPi uses one PCB takeoff for both existing USB ports if this header is connected to e.g., a 2-way hub it does the same job - there is no need for a second onboard header.
Now waiting for a similar article on replacing the micro-USB power supply header with something more universal - like a couple of copper pins or a connector block like http://www.cosam.org/images/a1200t/connector_block.jpg