In my month or so split between riding a motorcycle and taking trains throughout France in the past four years, here's what I've found:
- Takes magnetic strip + signature: Any place that takes credit card and has a live person collecting payment (e.g. cashier, waiter, etc). This means just about all stores, restaurants, manned gasoline stations and manned ticket booths will accept mag+signature, as well as chip+pin.
- Does not take mag strip+signature: most gasoline stations after hours, bicycle rental kiosks, metro ticket kiosks and train ticket kiosks. Essentially any self-service payment place. Many of these do not take cash either.
Pay particular attention to your gasoline level and time of day. I got stuck at gasoline stations after hours more than once. Locals could gas up with chip+pin cards. I didn't have one so I had to convince them to dip their card and take my cash in exchange. I was really glad I carried enough cash to get me to the next pillow.
Another thing to watch out for is that, in the US, some banks have EMV cards that are chip+signature rather than chip+pin. It's confusing because those chip+signature cards may have a PIN setup but that PIN does not work with the chip+pin system. Also, some web sites might mis-report them as chip+pin. As of May 2012, this was the case with the British Airways Visa Signature EMV card. Before you get a US EMV card, interrogate the bank to make sure it's chip+pin rather than chip+signature and that it can be used an unmanned kiosks in Europe that only accept chip+pin.
You might be able to find legit chip+pin EMV cards in the US from some credit unions like the Andrews Federal Credit Union. Their GlobeTrek Rewards Visa is the one I ended up with. See also Victoria Hawkins' blog and Flyertalk's forums for more good info on US banks and chip+pin.