It varies a lot. Last time I was in Paris there were people who were easy to deal with, and people who weren't. I can typically start a conversation in French, and carry out simple tasks like ordering/buying things, asking for directions. And that seems to help a lot, as does the fact that I've been told I have a Québecois accent (my first immersion in French was on a trip to Québec) and so I probably get taken for Canadian rather than American. But there are still many people whose entire attitude changes when they hear someone walking in and holding a conversation in English before switching to French, and I've actually been unable to get a table at a restaurant, or get help finding something in a store, when that happened.