Just got back from a four-night trip and, since I use this board for pretty much any vacation, though it was time to start contributing:
Fiamma - we had the Winter Tasting Menu at the MGM-Grand's Fiamma Trattoria. Osso Bucco and then a black truffle fusilli w/ prosciutto. Excellent wine service (they didn't try to sell us on anything expensive), plus they opened up a spot in the back for us to get away from the smoke from the casino. Both main courses were outstanding. Highly recommend the calamari too as an app. They worked hard to make sure we enjoyed the meal.
Il Fornaio - walked across from the MGM for some fresh fruit and fresh baked pastries. Worth the walk. Coffee was good too.
Enoteca Antipasti Bar - another great chef's tasting. We split it and each got the wine pairings. A little of everything and plenty of food. Ate a little sushi that night at Ra to top it off.
Bouchon - white boudin and the gratin du jour. Simple, great breakfast. We thought about going back immediately.
Mon Ami Gabi - the best thing we tried was the mussels app. I recommend getting a bottle of "by the glass" Beaujolais for $28 and enjoying it with a bowl of soup and the mussels while watching the Bellagio fountains. Our waiter told us they turn the 2nd most tables in a year in Vegas behind only Tao. You can get better mains elsewhere.
The Wynn Buffet - good. Go at 10:30 and you can effectively have brunch by waiting on the lunch menu to come out at 11:00. They don't mind at all if you linger, and the $7 unlimited mimosas encourages that too.
Cafe BaBaReeba - really impressed with their spanish reds + tapas at happy hour. Bacon wrapped dates and the serrano ham and manchego plate were both great. Chicken empenada was good too.
Enjoyed all of the meals. The only "must do again" was Bouchon's breakfast. If I was in the Venetian in the afternoon, I would definitely enjoy Enoteca again but probably wouldn't make a special trip. Hope that helps!