I am considering booking a reservation with Lufthansa/United in June 2013 The Lufthansa flight leaves Nice at 10:55am arriving in FRA at 12:45pm The connecting flight on United to SFO leaves at 2:00pm. (This option is on the United website.) My question is: Is 1 hour and 15 min enough time to catch the connecting flight?
Also, since I am coming from France, will I have to go thru customs in the Frankfurt airport in order to catch my flight to the US?
You should not have to go through customs since you are leaving the EU. However, there should be outgoing immigration since you are leaving the Schengen zone. At this time Frankfurt airport is not showing concourses, but in October the 12:45 flight from Nice comes into Terminal 1. Terminal 1 has three concourses. If both flights use the same concourse, changing gates should not be difficult. Right after 911, I came into FRA on concourse A and left on concourse B. Security was high, and I had to go through it three times and made the change in an hour. Something else to consider, if your luggage is checked through, and you have not shown up for the flight, they can't leave with your luggage on the plane and you not. They'll know you're making the change and probably wait for you. Otherwise they have to search for your luggage and take it off.
The official minimum connecting time in Frankfurt is 45 minutes. That means that both the airline as well as the airport guarantee that you will make your connection - or get onto another flight to SFO at no additional charge in a worst case scenario. In a few weeks all reconstruction at FRA's Terminal 1 will be finished and then the non-Schengen Gates are one floor above the Schengen gates - which means very short walks (actually just escalator rides and passport control). But yes, you will go through passport control in Frankfurt as well as through another security check (for US- and Israel-bound flights).