How much French should we be able to speak? Our advise here is: visibly making an effort to speak the language is much more important than your actual ability. A person with some ability but who is afraid to use it (because they are embarrassed to speak badly) is often perceived as arrogant, while a person who fumbles through a phrase book and butchers the language is often perceived as trying (they may laugh at you, but they will then help you).
There are, of course, the exceptional rude persons anywhere. France is actually famous for them, but that's more for the quality of the rudeness rather than the frequency.
To actually answer the question, you'll be able to use English in the larger towns, especially in the stores and shops. Hotels and restaurants are usually multilingual, and even in the villages hotel and restaurant staff can scrape up enough English when necessary. Again, you'll get better help with understanding your English if you try a bit of French first.
Comments contributed by Judy Hopkins, May 2001:
Some of my favorite times involved making do with my extremely limited French. Returning to Aix after Monte Carlo, we couldn't find our usual entry point to town and finally flagged down a policeman who told us to follow him, and sure enough, he led us to the hotel. A few hours later, when we left town at 4:00 a.m. headed for the airport, the signs at the traffic circle didn't point to Marseille as the hotel desk clerk had said. In a panic, we finally found a taxi driver who led us through the deserted streets of Aix as he delivered one fare, picked up another, and finally dropped us off at a traffic circle where he got out of his cab and explained how to get to the airport. We had a tense half hour as we drove along a deserted road that didn't look remotely familiar, but finally we saw some lights and the airport actually was there.