Which countries where Diners is very active in 2010?
 

I am puzzled where do they use Diners very actively in large numbers?

Some gas station in Italy...Pulled out the Amex "no", Puled out the Visa "no" Pulled out the Mastercard "no" In my best Itialian I asked what he took.."Dinners Club". I just handed the man my wallet and let him pull out french francs. I have not idea where I was just that was driving towards the Swiss Alps.

This is a challenging question to answer because Diners Club has two strands. The Diners Club cards issued in Canada and the USA are Mastercards, which brings broad acceptance (but would exclude Centurion's petrol station). Cards issued elsewhere are processed by Diners' proprietary network which is now owned by Discover.

So this happened at least ~9 years ago, correct? Either that or the francs in your wallet were Swiss...

Croatia, the company has almost 500000 issued cards and holds almost 38% of the market. Acceptance is almost 99,7% it means everywhere.
This is Diners Club Heaven. Believe me.
They have variety of cards, whatever you want.
The only minus is rewards program. They dont have so many bonuses with airlines.
http://www.diners.com.hr
The same situation is in Slovenia.

Austria is pretty good as well. VISA is larger and more accepted, but Diners is not bad.

I think Diners is gaining market share there by issuing co-branded cards (like with Austrian Airlines or the wine store chain Wein&Co).

certainly not in france, have just been there for two weeks and not any restaurant or other place accepted it...
slighty better in Italy, and even more so in Poland.
Sweden nah, here and there but Amex isn't widely accepted either (too high fees)
Spain, here and there, some gas station some restaurants

In which country is your card issued?

In Switzerland, Diners Club is working quite well as well.

Diners (the non-MC kind) is accepted pretty much everywhere in Brasil.

Here in Greece Diners Club is at a very good level. Comes third after Visa and MC but has a big portion of members mainly due to its history. Nowadays it has 5 personal logos, 2 premium logos and 2 corporate logos. Acceptance is very high especially since the implementation of a cardlink program that allows new card POS to send any transaction to any bank issuer. The only negative is the absence of Club Rewards but still has the Dine Diners programs that has similarities with the Diners Restaurant Savings program that was in US before the Mastercard alliance. In Cyprus acceptance is almost 100% but there are a few cardholders due to the fact that there isn't a issuer.

Diners acceptance is reasonably high in Brazil, as well. Due to changes in the acceptance networks in 2010, it was harder to use the card for about a year. But yesterday Diners signed an agreement with the largest acceptance network and now anyone who accepts credit cards should generally accept Diners.

The new network is called CIELO, by coincidence or not the surname of Brazil's very popular swimming champion César Cielo. In principle, it can accept any card, including even American Express, but a local merchant who has a CIELO terminal must still make arrangements to accept each card individually. So, although American Express, for example, advertises that 'you can use your card wherever there is a CIELO terminal', it's not really true.