Wow, lot's of opposing opinions out there.
So here's my two cents:
Yes, it does matter! For those of you saying, it doesn't matter how others dress, I say you are fooling yourselves. To place some perspective on that statement think of service.
Along with the casualness that today's society has adopted, we have also accepted much worse service. I waited tables 25 years ago while attending college. The service I typically receive today would have earned a reprimand 25 years ago. And today a higher tip is expected!!
Well we've seen that same decline in the dining rooms on ships: less service and automatic tipping. Imagine what kind of service you would receive in a dining room full of people dressed in bathing suits and sandles.
When I'm wearing my tux and my lovely wife is in an evening gown, I wanted to treated and served accordingly. Those of you that don't mind your dining room mates in beach casual, please remember that soon you will be served as if you are wearing beach casual.
I once had Italian dressing dumped down the sleeve of my tux. The waiter didn't offer to do more than wipe it off. My wife immediately summoned the headwaiter to explain the situation. She asked if we dressed like we didn't care! The line dry cleaned my tux. I think the waiter's lack of professionalism was due to laxed standards.
I dress to the situation in which I wish to immerse myself. People tend to conduct themselves better and receive better table service in a formal environment.
To those of you are fine with the dining room relaxing the dress code, please go eat in a casual dining room. If there's a dress code, please enforce it. If there are no dress codes or HAL drops formal nights, than so be it. I sail HAL because it is a bit dressier and elegant. I can go Jimmy buffet style and sail Carnival. Or if HAL does eliminate formal nights, I will choose a line that still has and enforces them. Currently only price influences my choice of HAL over Celebrity.
I'm not imposing my opinion on others, I'm just letting the cruiselines know how I choose. I expect formal night to be formal. If you choose not to be formal, there are other dining venues to choose. If the cruiseline chooses not to be formal there are other cruise choices.
Someone mentioned that casual is the direction the lines are going and we can't stop it. I agree with the first part of the statement, but not the second. The cruiselines are trying to make crusing available to the masses by lowering prices. 20 years ago, much fewer people could afford cruising. That same demographic enjoyed dressing. The masses don't enjoy dressing. HAL offers a product that Carnival does not. CCL (the whole corporation) will tailor the different lines to appeal to disctinct audiences. Windjammer/Carnival/HAL/Cunard each appeal to different groups. If they blurr the distinctions, they will become competitors.
If indeed, as this thread has read, people prefer to maintain the elegance that HAL offers without jumping to the cost of a Cunard sailing, then they will speak through their comment cards and influence HAL to keep and enforce formal nights.