I've been to sambuca twice for dinner and both times I split the $25 prix-fixe with a friend. The waitress was very nice about it, but I felt a little guilty because other than my table there was only one other diner. However, the servings are really big and plenty for two hungry females. We had the mussels, which were delicious and piled high in an addictive sauce, the steak (med-rare), which was big and juicy and paired with mashed potatoes and veggies on the side, and the creme brulee, which was in a big dish instead of the usual ramekin.
Another time, I've been here for lunch. I sat out in the patio and ordered a mango mimosa and a salad. The salad was gigantic and I remember struggling to finish it. I can't remember what kind of salad it was though.
I would recommend this restaurant for the great food and large portions. However, being on a student budget, I would probably go with a friend and split a meal again.