Congrats on your upcoming surgery! I had mine on Mon. 6/21/10! I am happy to say that the water weight from the IV's was not bad, about 5 pounds. Since my surgery I have lost a total of 10lbs from my weigh in before surgery.
My advice is to go to the hospital really hydrated. My goal was 68oz. a day pre-surgery and I kept to that right up until the no liquids cut off, the night before.
I felt really good after surgery and continue to feel good. I definitely tire easily, but I am walking a few blocks 3x a day and I think that has helped, too.
I have progressed to liquids like strained soups and cream of wheat, which makes me feel so much better. Have not felt hungry, but feel pretty full after that 2 oz. of soup!
Good luck and keep us all posted on your progress!