It may well be that the right firm, in the right part of France (the South is normally a little friendlier), you're going to be fine. In Paris though? It seems like it is almost a national sport to be a little rude to non-native speakers, and a lot more rude to people who just try and get by in English.
But if you're planning to move to France, to start a French start-up business, and employ French employees, it is probably a good idea to learn some French.
As an English speaker, the michelthomas.com courses point out that you already know a lot more French than you think. :-)
This may have been true at one point in time, but it's certainly no longer the case. I think this myth comes from a mix of two things:
a) differences in intonation that some people (mostly Americans) interpret as aggressive or hostile, when really they're not
b) the possibility that this was true in the past (e.g. during the 50's, perhaps because the French were eager to see stationed GIs leave)
That said, you'll get by, meet a lot of nice people from all over, get to vacation regularly in places which are "once in a lifetime travels" for most Americans, etc.
Or amybe, you know, because of the historical rivalry between France and England :)