We have sailed Crystal 8 times thus far and we love it. As far as informal nights are concerned a tie is not necessary however a sport jacket and slacks are the norm. Some of the more senior cruisers adorned ties. You will not feel out of place with a nice shirt jacket and slacks. Formal nights are just that and I have never seen anyone go back and change to casual after dinner. On our last cruise to south America we had three formal nights. On one formal night we opted for room service and videos and stayed in our very comfy robes. Enjoy the Crysatl experience!!!