I've just discovered this board! I was delighted to find some entries on Stuart, Jensen Beach, and Port St. Lucie. I agree with everything everybody said about Le Brittany (one of the best restaurants in the area), but I was very surprised that no one has mentioned Casa Bella. It's a great restaurant in Stuart and just as reliable as Le Brittany for excellent food. It's just off US 1 after you cross the Roosevelt Bridge (turn right after the bridge and then down your first left and you'll see it). It's in an old house and has a delightful atmosphere as well as great food.
Another place I'm becoming fond of is called Josef's in PSL. It's new and I've only been there twice so far, but I thoroughly enjoyed it both times. It's in the Morningside Shops plaza on the corner of Port St. Lucie Blvd and Morningside.