I got back on Sunday from a 10-day trip to Paris (yes, the one in France). It was a wonderful trip and I had an awesome time.
Part of what made the trip so wonderful is that the people of Paris are so nice. Really, they are. Forget everything you've heard about them hating Americans; it's just not true. Or at least, that was not my experience.
If you walk into a shop that sells clothing or fine linens while you are carrying a cup of coffee from Starbucks (yes, it's available), you don't say "Bonjour" to anyone, and you begin to demand immediate attention, you will get the stink eye. And you should. In America, where the customer is always right and the shops are staffed by people who are often trained only to use the register, that behavior is tolerated. (It's still horribly impolite, however, and please note that if I am in the shop at that time, I am judging you.) In France, where shopkeeping and waiting tables are professions, and people are proud to do an excellent job, it is not.
I found that making an effort to speak French (and my French is very, very limited) was appreciated. Most people switched to English immediately and seemed happy to do so. Maybe they wanted to practice their English, maybe they wanted to make things easier -- or maybe they just couldn't stand to hear me butcher their beautiful language. But they were polite and friendly about it, and I appreciated it.
Bottom line: in this, as in so many other things, your mother was right. Manners count.