DPs from a recent trip to Europe:

Prague:

• Euronet ATM at airport offered conversion with somewhere in the neighborhood of 8% markup IIRC in addition to 2000 CZK minimum withdrawal (~90 usd including fee)
• Other bank ATMs offered conversion with smaller 3-4% markup
• ATM choices to debit in CZK were respected
• No DCC encountered elsewhere (restaurants, regular retail shops)

Munich: No DCC offered at bank ATMs, regular shops

Switzerland:

• DCC offered only at railway ticket windows and machines at a 3-4% markup. Choice to debit in CHF respected
• No bank ATM DCC
• No DCC encountered otherwise

Got to wonder how many suckers would accept DCC in Switzerland with a USD denominated card, given CHF is essentially pegged to USD.