Most EU countries have not been problematic. Any place that accepts any Visa will usually accept a US swipe & sign Visa. Same for MC, AMEX, etc. There were some problems in the UK in 2006 with merchants being confused but this was somewhat cleared up within a few months.

However, problems with non chip&pin are growing again. Particularly in the UK but also to some extent in FR, NL, and BE. Within tourist areas there appear to be few problems but outside tourist areas where they don't often see US cards it's becoming a different story. Some merchants will refuse to take non C&P cards though most will give in if you point out that you know that's in violation of their merchant agreement. The bigger problem for these and other merchants is that many simply don't know how to deal with a swipe & sign xaction, particularly restaurants where a tip is involved.

At the Waitrose in South Kensington 2 people spent 20 minutes trying to figure it out and were finally walked through it with telephone support. Of 5 restaurants 2 had no problems 1 took an extra few minutes to find the manager who knew how to do it and 2 took over 20 minutes (with one running up the street to his friends restaurant who knew how).

Most non-attended petrol stations only take C&P. I believe this goes for auto ticket machines in train and tube stations as well though at least for the tube you can still use cash. I have an auto top up Oyster so this wasn't a problem for me.

I thought NL rail had always been NL only cards except the ones at Schipol.