Turin: definitely yes on the liquid chocolate. Everybody goes there, and I don't know if it's the best in Turin, but it's worth it and you won't really care.
Venice: start
here most of the way down the page. A short version of those contents: Corte Sconta, definitely. It's not hard to find, precisely, but it's very easy to not see even if you're right next to, or right around the corner from, the place. Make a reservation.
I did not particularly enjoy the highly-regarded Osteria La Zucca, but mine has been the minority opinion.
Busa alla Torre (Campo San Stefano 3, Murano) is more worth the trip out there than the shops full of the finest Chinese glass, I think. Oh, and Burano and the incomparable Torcello are
definitely worth the complication of getting there.
Finally, you should do the shadow stuff pre-dinner, if you can. We had a fabulous time at El Refolo (you'll find the info in part 7 of the linked travelogue) by asking if we could have plates of local delicacies and whichever local wines the proprietor was most proud of, but I'm sure this experience can be replicated elsewhere, albeit with fewer locals.
Da Ivo was highly recommended by several in the Piedmont this past week, but I haven't been. Vini da Gigio has a fabulous wine list as well, but the food is only good enough...or at least was at the beginning of the 00s, when I was last there.
You have to do more restaurant research for Venice than perhaps anywhere else in the world (well, maybe Bhutan...), but it's very possible to avoid bad meals. And even if you must have a lunch pizza on the water, as long as you have it somewhere other than on the Grand Canal or on the tourist axis (train station - Rialto Bridge - Piazza San Marco) you can easily get something quite competent. People who eat nothing but overpriced & lousy food in Venice didn't try very hard. I mean, it's hard to say and harder to hear, but it's true, and in the everything-is-reviewed-by-someone era, there's no lack of guiding sources.
Levi's right about the pricing structure. Oswaldo is right in that it is
essential to get lost in Venice. GPS doesn't work very well, though, in the narrow and twisty streets where you'll need it most. Buy a good map.
It's absolutely one of my favorite places in the world, but the real magic happens after all the ships leave for the night, far from the major tourist sites, and wherever you find people walking purposefully and without maps. I cannot stress enough: go in the off-season. Almost everyone I know who has been to Venice and hated it (a fair number of people), made the same three mistakes: summer, no restaurant research, saw/did only The Sites. No, you can't miss the Basilica San Marco (take all the optional tours, despite the extra cost). Yes, you should get the $30 espresso on the Piazza at whatever that gilded temple of coffee is (drink it inside, not outside). Yes, you should tour the Doge's Palace (book ahead if you can). And that will all take a day, given the length of the lines. Spend the rest of your doing something much more interesting and aimless. You'll be glad you did.