Are the Mt.Gox markets for different currencies completely separated? MtGox supports multiple currencies. Usually referred to as f.e. mtgoxUSD, mtgoxEUR, ...

Now, MtGox has different market depth listings for it's different markets and keeps a separate price for them.

Are these markets completely separated, meaning that when I place a buying order in euros, it can only be matched with selling orders in euro? This would also mean that less popular markets inside MtGox, which have less average volume, can have the same delay effects as less volumous non-MtGox markets in let's say US dollars?

So, is it possible that I buy bitcoins with euros and that someone else receives dollars for the coins I bought?
There is only one order book in MtGox. Orders aren't segregated by currency, rather, all prices are relative to the currency with the highest volume (based off The European Central Bank's daily rates). In their own words,


  For example, if a buy order for bitcoins is placed in EUR, the order can be executed against another user selling bitcoins in any currency and not necessarily only against another user selling bitcoins in EUR.


That said, wallet currencies are completely separate. There's no converting between them unless you're transferring that value via bitcoins themselves. For example, you can buy bitcoins in a EUR wallet with EUR, transfer them to a USD wallet and sell them in USD. Of course, you have to consider how you'll withdraw the resulting currency.