I go to Cozumel annually for a dive trip. STICK TO THE BOTTLED WATER. WATCH OUT FOR ICE IN MIXED DRINKS. WAIT TIL YOU GET HOME TO HAVE THE SALAD.
There are some restaurants that are real safe but your stomach is experiencing new foods and suceptable to upset. Last year, as always I was very careful and was fine- my son decided to try the salsa at a beach restaurant and had a most uncomfortable nite.
I traveled to Sicely last year and had more problems than I've ever had in Mexico.
Good Luck
Bart

I've travelled throughout Mexico and have a VERY sensitive system... the only thing that works for me is to take along a bottle of Pepto-Bismol and take a dose before each meal. I eat whatever I want then but stick to bottled water and it works for me. Make sure to buy the Pepto before you leave because it is hard to find and more expensive in Mexico.

Follow the precautions for 3rd world countries. It is the luck of the draw. We once went to the Yucatan almost every year. The last time we were in Akumal (near Tulum) fully 50% of the people staying at our resort were ill. Don't eat any raw items that you don't peal yourself. Use only bottled water that has been sealed and opened by yourself. Don't drink anything that has or once had ice in it. Get hepititus A shots.

I just got back from a week in Playa Del Carmen at the Iberostar and was really nervous about getting sick, as I don't have a very good stomach. I ate everything -- salad, ice cubes, not a problem! I ate in town, at my hotel, and at the tourist sites. Stick to bottled water instead of tap, but otherwise, if you are at a hotel that caters to tourists, you'll be fine (everyone was eating salad).

Ditto everything that Jen said. We just got back from two weeks at the RIU Yucatan which is next door to Iberostar.
You have to figure that the last thing any of the resorts want is to have a bunch of ill people on the resort, so EVERYTHING on the resort is going to be safe to drink or eat. But yes, stick to bottled water (available in copious amounts in our in-room mini-bar by the way) and if you go into PDC and stop at one of the dining or drinking spots, perhaps you should stick to bottled drinks only if you have any kind of a sensitive stomach. Think about this - if the washroom at a particular place looks like a nightmare, then do you really want to chance eating a meal there??
My husband and I both got a bit of trots but what can you expect from two weeks of double espressos, creamy cappaccinos, copious amounts of rich food, tonnes of fresh fruit, creamy boozy drinks, and excess amounts of alcohol, eh!
In Mexico, everyone is eating and drinking foods and beverages that they are just not used to, so go figure that a little of Imodium or Pepto Bismal is needed to settle things down a bit!
So don't panic - go, eat, drink and be merry and religiously wash your hands after using the washroom (which you do anyhow, right!)