I had this at the Carluccio's summer menu launch and absolutely loved it. It sounds odd at first, but in the words of Joey from Friends, limoncello: gooood, limonata: gooood, prosecco: gooood. It's light, incredibly lemony and scarily drinkable. It might even replace the Aperol spritz as my new summer drink.
If anyone's got any of my wedding favour limoncello left over, I suggest you make yourself one of these. One shot of limoncello and then top up with half and half of San Pellegrino limonata and prosecco = summer in a glass. Now take me to Sicily.